TEL AVIV – Israel's senior military intelligence analyst said Tuesday there was evidence the Syrian government had repeatedly used chemical weapons in the last month, and he criticized the international community for failing to respond, intensifying pressure on the Obama administration to intervene.
"The regime has increasingly used chemical weapons," said Brig. Gen. Itai Brun, research commander in the intelligence directorate of the Israeli Defense Forces, echoing assertions made by Britain and France. "The very fact that they have used chemical weapons without any appropriate reaction," he added, "is a very worrying development, because it might signal that this is legitimate."
General Brun's statements, made at a security conference here, are the most definitive by an Israeli official to date regarding evidence of possible chemical weapons attacks on March 19 near Aleppo and Damascus. Another military official, speaking on the condition of anonymity, said that the evidence had been presented to the Obama administration -- which has declared the use of chemicals a "red line" that could prompt American action in Syria -- but that Washington has not fully accepted the analysis.
None of the assertions -- by Israel, Britain or France -- have been made with physical proof of chemical weapons use. Experts say the most definitive way to prove the use of chemical weapons is to promptly gain access to the site to collect soil samples and examine suspected victims.
The Syrian government, which has accused insurgents of using chemical weapons and has requested that a United Nations forensics team investigate, has so far refused to allow that team to enter because of a dispute over the scope of its inquiry.
In Brussels, at a meeting of NATO foreign ministers, Secretary of State John Kerry urged that members of the alliance be ready to respond if it is determined that Syria had in fact used chemical weapons.
"We should also carefully and collectively consider how NATO is prepared to respond to protect its members from a Syrian threat, including any potential chemical weapons threat," Mr. Kerry said. He did not specify in his publicly released remarks what planning he wanted from members of the NATO alliance.
Mr. Kerry was one of several American officials who reiterated on Tuesday that Washington was not yet convinced there had been chemical weapons use, and he suggested there were mixed messages even coming out of Israel. He said he had talked by telephone Tuesday morning with Prime Minister Benjamin Netanyahu of Israel, and "he was not in a position to confirm that in the conversation that I had."
"I don't know yet what the facts are," Mr. Kerry added. "I don't think anybody knows what they are."
A spokesman for Mr. Netanyahu refused to comment on the telephone call on the apparent disconnect between the prime minister and his military leaders.
In briefings earlier on Tuesday, the Israelis said they believed that the attacks March 19 involved the use of sarin gas, the same agent used in a 1995 attack in the Tokyo subway that killed 13.
The Syrian attacks killed "a couple of dozens," the military official said, in what Israel judged as "a test" by President Bashar al-Assad of the international community's response. He said the government had deployed chemicals a handful of times since, but that details of those attacks were sketchier.
"Their fear of using it is much lower than before using it," the official said. "If somebody would take any reaction, maybe it would deter them from using it again." Regarding possible further attacks, he added, "Now I'm more worried than I was before."
Israel, which is in a technical state of war with Syria, has been deeply reluctant to act on its own in Syria, for fear that it could bolster President Assad by uniting anti-Israel sentiment. But the public statements regarding the attacks, days after the British and French governments wrote to the United Nations Secretary General saying they, too, had evidence of chemical use, complicates the situation for Washington.
President Obama said last month during his visit to Israel that proof of chemical weapons use would be a "game changer." But Defense Secretary Chuck Hagel said Monday that the intelligence regarding the attacks remained inconclusive, and his press secretary, George Little, said Tuesday that the Pentagon was continuing to assess reports on the matter.
"The use of such weapons would be entirely unacceptable," Mr. Little said in Amman, Jordan, where Mr. Hagel landed Tuesday. "We reiterate in the strongest possible terms the obligations of the Syrian regime to safeguard its chemical weapons stockpiles, and not to use or transfer such weapons to terrorist groups like Hezbollah."
Speaking about Syria at a conference of Israel's Institute for National Security Studies here, General Brun said "it is quite clear that they used harmful chemical weapons," citing "different signs" including pictures of Syrians, said to be victims, "foaming at the mouth." He went beyond the March 19 attack to speak of "continuous" use of such weapons, and described a "huge arsenal" of more than 1,000 tons stockpiled in Syria.
Speaking at the same security conference, the United States ambassador to Israel, Daniel B. Shapiro, said the United States was still "seeking the fullest and most accurate assessments" from American intelligence agencies, but added that the "contingency plans" for addressing the use of chemical weapons in Syria was "very much part" of discussions between Mr. Hagel and his Israeli counterpart here on Monday.
The Israeli military official who spoke on the condition of anonymity said that Israel based its analysis mainly on what he described as publicly available photographs of victims, but said there was also corroborating "direct evidence" that he would not detail.
The United States has also made efforts to gather evidence from the field, although no outside authority has direct access to the sites of suspected use.
Majid, a rebel commander from the eastern suburbs of Damascus, said his battalion had been contacted, through intermediaries, by the Central Intelligence Agency, requesting samples to be tested for the presence of chemicals. Speaking via Skype from Jordan, and on the condition he be identified only by first name for his safety, Majid said the American intelligence agency had requested soil, urine and hair samples from several areas around Damascus: Jobar, a northeastern neighborhood of the city that has been fiercely contested in recent months; Adra, an industrial area north of the city; and Ataibeh, northeast of the capital.
"We're still waiting to get the samples," Majid said, explaining that it would take time because of the difficulty of traveling to contested areas.
Louay Mekdad, a spokesman for the Free Syrian Army, has also said the umbrella group of rebels would collect evidence of the attacks, including testimony from doctors and patients and physical samples.
Though the Assad government had claimed last month that it was the rebels who used chemicals, General Brun echoed previous statements by Israeli and American officials that such claims were not credible.
Israeli military officials said that over the past few months that they believe Syria had sharply consolidated its chemical stockpiles, reducing the number of sites by about half to retain greater control over the arsenal. The weapons are now stored in 15 to 20 sites, they said.
If American officials have been more reluctant that their allies to come to firm conclusions, it may be because it would force Mr. Obama's hand. In August, the president told reporters that any evidence that Mr. Assad was moving the weapons or making use of them could prompt the United States to act.
"That would change my calculus," he said. "That would change my equation."
But when strong evidence emerged earlier this year that Mr. Assad's forces were in fact moving their weapons -- at least from one depot to another -- the White House insisted that the action did not cross the line that Mr. Obama set. By "move" the weapons, a White House spokesman said, Mr. Obama meant transferring them to a militant group, like Hezbollah.
Nonetheless, according to two American officials, Washington sent messages to President Assad that the threat had to be taken seriously. "We saw a reaction," one official said. Protection of the sites was improved. While the United States has drawn up plans to seize control of the weapons if need be -- by parachuting in troops to the key sites -- American officials have made it clear that they would prefer that regional forces take the lead. But if the weapons were actually used, as three American allies now contend, it would be far more difficult for Mr. Obama to argue that his "red line" has not been crossed.
Israel, which in January bombed a convoy of sophisticated antiaircraft weapons it feared was being transferred from Syria to Hezbollah in Lebanon, has been preparing its own plans, though it far prefers a broader international intervention.
"There is a risk that if Israel will do something there will be no international community or coalition," said the Israeli military official. "Maybe because Israel is so close Israel sees it differently from the rest of the world. Just imagine if there was a use of chemical weapons in Mexico. Everyone in the southern United States would be very worried about that."
The Syrian government has never publicly acknowledged that it has chemical weapons, stating simply that it would never use chemical weapons, if it had them, against its own people. But in July, a prominent government spokesman, Jihad Makdissi, raised eyebrows earlier in the conflict by saying that Syria would use chemical weapons only against a foreign attacker, not against its own people. But he also noted that Syria was facing external enemies as part of the conflict.
Some read his wording as an admission that Syria had the weapons. Others noted that since Syria's government has characterized its armed opponents as foreign and foreign-inspired terrorists, the statement might be laying the groundwork to justify using the weapons against the uprising.
Mr. Makdissi later took a less prominent role and fled the country five months later.
Reporting was contributed by Thom Shanker from Amman, Jordan, Hwaida Saad from Beirut, Lebanon, and Michael R. Gordon from Brussels.
This article originally appeared in The New York Times.