WASHINGTON — President Obama warned Syria’s government Monday that it would be ‘‘totally unacceptable’’ to use chemical weapons against its own people and vowed to hold accountable anyone who did, as US 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 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. 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, 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 Obama would go that far.
“Today I want to make it absolutely clear to Assad and those under his command: The world is watching,’’ 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.’’
The warning from the White House came as developments elsewhere suggested the political terrain could be shifting. A senior Turkish official said that Russia had agreed Monday to a new diplomatic approach that would seek ways to persuade Assad to relinquish power, a possible weakening in Russia’s steadfast support for the government.
During an earlier briefing at the White House, Jay Carney, the president’s press secretary, hinted at possible military action in response to any use of chemical weapons, although he declined to specify what options Obama would consider.
“We think it is important to prepare for all scenarios,’’ Carney said. ‘‘Contingency planning is the responsible thing to do.’’
The president’s statements on Syria amplified similar warnings issued by Clinton earlier in the day in Prague, where she was stopping on her way to meetings in Brussels.
“This is a red line for the United States,’’ Clinton said, using the same language that the White House would use later. ‘‘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 US and Israeli officials familiar with intelligence reports. 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.
After meeting in Istanbul on Monday, President Vladimir V. Putin of Russia and President Recep Tayyip Erdogan of Turkey said they had agreed on a new approach to resolving the conflict.
‘'We are neither protecting the regime in Syria nor acting as their advocate, but remain worried about Syria’s future,’’ Putin said at a joint news conference with Erdogan.
Putin did not elaborate, though Mikhail Bogdanov, a deputy foreign minister, said Russia would meet intensively with Syrian opposition groups based inside the country in the coming month. A senior Turkish official, speaking anonymously, said plans included looking for ways to get Assad to step down. There were still no firm indications from Russia that it was ready to insist on Assad’s immediate departure.
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. Fighting raged around Damascus, the Syrian capital, and its airport Monday, disrupting commercial flights for a fourth straight day.
The United Nations regional humanitarian coordinator for Syria, Radhouane Nouicer, said the UN is pulling nonessential international staff out of the country because of the security situation, the Associated Press reported. Up to a quarter of the 100 international staff working for several UN agencies could leave by week’s end. There are 900 more local staff members working for the UN in Syria.
Lebanon’s Al-Manar television reported that a Syrian Foreign Ministry spokesman, Jihad Makdissi, had been fired for making statements that did not reflect the government’s position. Activists said he had defected.