WASHINGTON -- Secretary of State John Kerry said Monday that the use of chemical weapons in attacks on civilians in Syria last week was undeniable and that the Obama administration would hold the Syrian government accountable for what he called a "moral obscenity" that had shocked the world's conscience.
In some of the most strident language used yet by the administration, Mr. Kerry accused the Syrian government of cynically seeking to cover up the use of the weapons, and he rejected its denial of responsibility for what he called a "cowardly crime."
Mr. Kerry's remarks, in a prepared statement he read at the State Department, reinforced the administration's toughening stance on the Syria conflict, which is now well into its third year, and he suggested that the White House was moving closer to a military response in consultation with America's allies.
"The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity," Mr. Kerry said.
"By any standard, it is inexcusable," he said. "And despite the excuses and equivocations that some have manufactured, it is undeniable."
Mr. Kerry also said the Syrian government's refusal to allow immediate access to the attack sites last Wednesday was a telling indicator that it was trying to hide responsibility. Even though a United Nations team was finally permitted by the Syrian government to investigate starting Monday, he said, the government's authorization was "too late" to be credible.
"Our sense of basic humanity is offended not only by this cowardly crime but also by the cynical attempt to cover it up," he said.
Mr. Kerry spoke hours after United Nations inspectors were finally allowed access to one of the attack sites, despite shooting from unidentified snipers that disabled their convoy's lead vehicle. The inspectors still managed to visit two hospitals, interview witnesses and doctors and collect patient samples for the first time since the attack last week that claimed hundreds of lives.
Secretary General Ban Ki-moon said in a statement that he had instructed his top disarmament official, Angela Kane, who was visiting Damascus, to register a "strong complaint to the Syrian government and authorities of opposition forces" to ensure the safety of the inspectors after the assault. There was no indication that any member of the inspection team had been hurt.
Mr. Ban's spokesman, Farhan Haq, told reporters at a regular daily briefing at United Nations headquarters in New York that the assailants, who had not been identified, fired on the first vehicle in the convoy, which was "hit in its tires and its front window, ultimately it was not able to travel further."
Antigovernment activists posted videos online of United Nations inspectors in blue helmets arriving in the Moadamiya area, southwest of the capital, where they were shown entering a clinic and interviewing patients.
Moadamiya is a rebel-held suburb where antigovernment activists reported the smaller of two suspected chemical attacks last Wednesday. Videos posted then showed patients in a rebel field hospital apparently having trouble breathing.
The visit by the United Nations inspectors to the Damascus suburb, in a half-dozen vehicles escorted by Syrian security forces, came shortly after President Bashar al-Assad of Syria denied that his forces had used poison gas against his own citizens, and as divisions between outside powers over how to handle the crisis showed no signs of easing.
In an interview with the Russian newspaper Izvestia, published on Monday, Mr. Assad said accusations that his forces had used chemical weapons were illogical and an "outrage against common sense." He warned the United States that military intervention in Syria would bring "failure just like in all the previous wars they waged, starting with Vietnam and up to the present day."
Mr. Assad's choice of a Russian newspaper to air his views seemed to reflect Moscow's strong support for the Syrian leader after last week's attack on the outskirts of Damascus, which claimed hundreds of lives.
On Sunday, a spokesman for Russia's Foreign Ministry, Aleksandr K. Lukashevich, said that those who advocated an armed response to any chemical weapons attack -- without citing the United States or other countries -- were prejudging the results of the United Nations inspections.
"In these conditions, we again resolutely call on all those who are trying to impose the results of the U.N. investigations and who say that armed actions against Syria is possible to show common sense and avoid tragic mistakes," Mr. Lukashevich said in a statement released on the ministry's Web site.
While Mr. Assad has said he would give weapons inspectors access to the site, the gesture has been greeted with widespread skepticism in the West, with critics saying that the offer came too late for inspectors to make an accurate assessment of what happened. The British foreign secretary, William Hague, complained on Monday that access was not "unimpeded" since it was limited to a "certain number of hours."
British officials also said on Monday that Prime Minister David Cameron would cut short a vacation in Cornwall, in southwest England, to return to London and head a meeting of senior ministers on Wednesday. His gesture seemed designed to heighten the mood of crisis as outside powers wrestle with Mr. Assad's refusal to bow to the West.
"If someone dreams about turning Syria into a puppet of the West, it simply will not happen," Mr. Assad told Izvestia. "We are an independent government, and we will battle with terrorism and we will freely build relations with those countries whom we want to."
In an interview Monday with Europe 1, a French radio station, Foreign Minister Laurent Fabius of France, said "all options" were still open in crafting an international response, but "the only option I do not envisage is to do nothing." France has been a close ally of the rebels seeking Mr. Assad's ouster in the country's civil war.
Mr. Fabius said there was no doubt that chemical weapons had been used and outside powers would negotiate a "proportionate response" in the "days to come."
In the welter of diplomatic maneuvering, Turkey, also a strong supporter of the rebels, said it would join an international coalition against Mr. Assad if the United Nations Security Council could not reach a consensus, Reuters reported, quoting Foreign Minister Ahmet Davutoglu in an interview with the Milliyet newspaper.
In London, Mr. Hague took a similar approach to an international response. "Is it possible to respond to chemical weapons without complete unity on the U.N. Security Council?" he told the BBC in a radio interview. "I would argue yes it is, otherwise it might be impossible to respond to such outrages, such crimes, and I don't think that's an acceptable situation."
Russia's foreign minister, Sergey V. Lavrov, warned against prejudgment about the use of chemical weapons, saying that the United States and other countries had already mistakenly drawn conclusions by raising the specter of punitive military strikes. As Russia has asserted previously, Mr. Lavrov suggested that the attacks had been orchestrated by the rebels or other nongovernmental forces, saying it was illogical that the Syrian government would have launched an attack that would prompt an international response.
Mr. Lavrov warned that any Western intervention would be a "serious mistake," evoking the experiences of interventions in Iraq and Libya in particular.
"If someone thinks that, having bombed the Syrian military infrastructure and having left the battlefield such that the enemies of the regime will seize victory, that all this will end, it's an illusion," Mr. Lavrov told reporters at the Foreign Ministry in Moscow. "Even if such a victory is achieved, the civil war will continue. "
He said that bypassing the United Nations Security Council to move militarily against the Syrian government would be "the grossest violation of international law" that would "sharply worsen the situation."
In the interview with Izvestia, Mr. Assad said, "America has taken part in many wars but could not once achieve its political goals for which the wars were started. Yes, it is true, the great powers can wage wars but can they win them?"
He said government troops would have risked killing their own forces if they had used chemical weapons. "This contradicts elementary logic," news reports quoted him as saying. It is "not us but our enemies who are using chemical weapons," he said, referring to antigovernment rebels as "the terrorists."
For his part, President Obama has not decided to take action, officials in Washington said on Sunday. But, moving a step closer to possible American military involvement in Syria, a senior Obama administration official said that there was "very little doubt" that Mr. Assad's military forces had used chemical weapons against civilians and that a Syrian promise to allow United Nations inspectors access to the site was "too late to be credible."
Chuck Hagel, the American defense secretary, said Monday during a trip to Indonesia that the United States was examining all options but would not act alone. Speaking to reporters, Mr. Hagel said: "if there is any action taken, it will be in concert with the international community and within the framework of legal justification."
In Israel, a senior government official said Monday it was "crystal clear" that Mr. Assad's forces used chemical weapons last week and called the United Nations investigation effort a "joke." The official said that Iran, a close ally of the Syrian leader, should also be held responsible.
"The world cannot allow this to proceed," Yuval Steinitz, Israel's minister of international affairs, strategy and intelligence, told international reporters at a briefing Monday morning in Jerusalem. "The Iranians are already trying to isolate themselves from the use of chemical weapons. This is a kind of hypocrisy. You cannot be part of this terrible, brutal war and say, 'Yeah, I participate in the war but I isolate myself, I separate myself from the use of chemical weapons.' Assad today is almost a total proxy to Iran."
Echoing other Israeli leaders, Mr. Steinitz suggested that the Syria situation was a kind of harbinger regarding Iran's disputed nuclear program. "If Iran would get nuclear weapons, it's going to create a new, very dangerous new world, this is a global game-changer," he said.
Regarding the United Nations inspectors' search for evidence that chemical weapons were used, Mr. Steinitz said, "This is becoming a joke."
Michael R. Gordon reported from Washington, Alan Cowell from London and Rick Gladstone from New York. Reporting was contributed by Andrew Roth and Noah Sneider from Moscow, Ben Hubbard from Beirut, Lebanon, and Jodi Rudoren from Jerusalem.
This article originally appeared in The New York Times.