WASHINGTON -- President Obama warned Syria's government on Monday that it would be "totally unacceptable" to use chemical weapons against its own people and vowed to hold accountable anyone who did, as American intelligence officials picked up signs that such arms might be deployed in the ongoing insurgency.
The White House said that some recent actions by the government of President Bashar al-Assad were indicators that Syrian forces were preparing to use such weapons, following earlier reports that intelligence agencies had noticed signs of activity at chemical weapons sites. Mr. Obama's spokesman said the administration had "an increased concern" of possible use of chemical weapons.
In a speech later in the day that echoed earlier comments by Secretary of State Hillary Rodham Clinton, Mr. Obama sternly asserted again that he would punish Syria for using chemical weapons, although he did not say how. The administration has been preparing contingency plans that include the dispatch of tens of thousands of troops to secure such weapons, although it is not clear whether Mr. Obama would go that far.
"Today I want to make it absolutely clear to Assad and those under his command: The world is watching," Mr. Obama said in a speech at the National Defense University in Washington. "The use of chemical weapons is and would be totally unacceptable. If you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable."
During an earlier briefing at the White House, Jay Carney, the president's press secretary, hinted at possible military action in response, although he declined to specify what options Mr. Obama would consider. "We think it is important to prepare for all scenarios," Mr. Carney said. "Contingency planning is the responsible thing to do."
The president's statements on Syria amplified similar warnings issued by Mrs. Clinton earlier in the day in Prague, the Czech capital, where she was stopping on her way to meetings in Brussels.
"This is a red line for the United States," Mrs. Clinton said, using the same language that the White House later would use. "I am not going to telegraph in any specifics what we would do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people. But suffice it to say we are certainly planning to take action if that eventuality were to occur."
There have been signs in recent days of heightened activity at some of Syria's chemical weapons sites, according to American and Israeli officials familiar with intelligence reports. Mrs. Clinton did not confirm the intelligence reports or say what sort of activity was occurring.
The Syrian Foreign Ministry, in a swift response, said the government "would not use chemical weapons, if it had them, against its own people under any circumstances." The statement was reported on Syrian state television and on the Lebanese channel LBC.
The crisis has been worsening in Syria, where about 40,000 people have been killed in 20 months of conflict that has also spilled into neighboring countries. The warning from the White House came as developments elsewhere suggested the political terrain could be shifting.
The spokesman for Syria's foreign ministry, Jihad Makdissi, was reported by the Hezbollah-run television station, Al Manar, as having been fired, although Lebanese news Web sites reported the departure as a defection. Mr. Makdissi, one of the highest ranking Christians to defect, had been one of the most accessible Syrian officials for foreign journalists. Al Manar reported that he was fired for making statements that did not reflect the government's point of view, though it was unclear what those statements might have been.
But in recent months he had not taken phone calls and had not made public statements, leading some to speculate that he had either fallen out of favor or had doubts about the government. A security source said Mr. Makdissi flew to London from Beirut on Monday morning with his family.
"If he defected or didn't defect, we don't know," Rami Abdulrahman, the director of the British based Syrian Observatory for Human Rights, which has a wide network of contacts in Syria, said.
Mr. Abdulrahman, who uses a pseudonym for safety, said Mr. Makdissi had angered some in the Syrian government by saying Syria would use chemical weapons only against a foreign invasion and not its own people; however, the government does not acknowledge that it has such weapons. Mr. Abdulrahman also said that some figures had become irritated with Mr. Makdissi's prominence.
Also on Monday, government officials in Turkey held talks in Istanbul with President Vladimir V. Putin of Russia, centered on the Syrian crisis.
Though he remained oblique in his statements at a joint news conference, Mr. Putin appeared to signal that Russia was easing away from its insistence in supporting Mr. Assad and that it was moving toward the position of Turkey and some other Western nations who have called for the Syrian leader to step aside.
"Our positions regarding what's happening in Syria and what should be done regarding its future are the same," Mr. Putin said at a news conference. "We have different viewpoints about how to reach to that point, so during our talks new ideas came up, which we will work on in near future."
One senior Turkish official noted a definite shift in the Russian attitude toward Mr. Assad's government. "There is definitely a softening of Russian political tone when they no longer insist on a resolution under the Assad rule," said the official, who declined to be named, following diplomatic protocol. "We agreed on common premises that democracy should be structured in Syria through legitimate elections, but the question is how to come to that point, especially when Assad doesn't seem to be willing to quit, which Putin also acknowledges."
In Syria, government warplanes launched airstrikes in rebel-held towns near the border with Turkey, including Ras al-Ayn. The Local Coordination Committees, an opposition group, said at least 10 people had been killed there.
On Monday, the United Nations regional humanitarian coordinator for Syria, Radhouane Nouicer, said that they were pulling nonessential international staff out of the country because of the security situation, The Associated Press reported.
Mrs. Clinton, who made her comments after meeting with Karel Schwarzenberg, the foreign minister of the Czech Republic, indicated that they had discussed the situation in Syria, including the potential chemical weapons threat. She later flew to Brussels for a NATO foreign ministers meeting.
Mr. Schwarzenberg described the situation in Syria as "rather chaotic" and "highly dangerous." He said that Czech troops who specialize in the detection of chemical weapons and decontamination were in Jordan training with forces there.
An American task force has been deployed to Jordan and has been helping the Jordanians deal with an escalating humanitarian crisis centered on Syria, including an exodus of more than 200,000 refugees from Syria to Jordan. The force is also planning how to respond, if necessary, to any chemical weapons threat.
Michael R. Gordon reported from Brussels. Reporting contributed by Anne Barnard from Beirut, Lebanon, and Sebnem Arsu from Istanbul.
This article originally appeared in The New York Times.