PRAGUE: US Secretary of State Hillary Clinton on Monday warned the regime of Bashar al-Assad against any bid to unleash chemical weapons on the Syrian people, signalling that the United States would be prepared to take unspecified action.

“This is a red line for the United States,” Clinton said after meeting Czech Foreign Minister Karel Schwarzenberg, during which they talked about concerns over Syria's chemical weapons stockpile.

“Once again we issue a very strong warning to the Assad regime that their behaviour is reprehensible. Their actions against their own people have been tragic,” she told a joint news conference with her Czech counterpart.

“I'm 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 that we're certainly planning to take action if that eventuality were to occur,” the top US diplomat stressed.

Clinton's remarks came as The New York Times reported Monday that the Americans and Europeans had sent warnings via intermediaries to the Syrian regime after detecting movement of chemical weapons by the Syrian military in recent days.

“The activity we are seeing suggests some potential chemical weapon preparation,” one US official told the daily, which added that the weekend activity set off a flurry of emergency communications among the Western allies.

The international community fears that Assad is becoming increasingly desperate as he seeks to defeat opposition rebels aiming to oust him.

But in Damascus, a foreign ministry spokesman said Syria would never deploy chemical weapons against its own people.

“Syria confirms repeatedly it will never, under any circumstances, use chemical weapons against its own people, if such weapons exist,” he said, quoted on state television.

Nato opens two days of talks Tuesday with the 21-month conflict in Syria, said to have claimed 41,000 lives, set to top the agenda.

Clinton said she discussed chemical weapons with her Czech counterpart and stressed that the Czech Republic “plays a key role in chemical, biological, radiological, and nuclear response” both in Nato and beyond.

“There is no doubt that there is a line between the horrors that they (the regime) have already inflicted on the Syrian people and moving to what would be an internationally condemned step of utilising chemical weapons,” she said.

Schwarzenberg stressed that the situation in Syria “is rather chaotic and we can't even exclude the case ... by chance, that one of the rebel groups would get hold of these arms. That, of course, would be a danger as well.”

The Atlantic magazine reported that the United States was not alone in its concerns about Syria's chemical weapon stock.

According to two officials from two other countries, Israel has sought permission from Jordan to bomb some of Syria's suspected chemical arms sites. Jordan has so far refused the request, which could require the use of its airspace.

“The Jordanians have to be very careful about provoking the regime and they assume the Syrians would suspect Jordanian complicity in an Israeli attack,”one of the officials told the magazine.

A US official confirmed to reporters travelling with Clinton that there were no plans to discuss a possible no-fly zone for Syria at the Nato talks.

However, the senior US State Department official said Washington was “hopeful that Nato will be in a position to respond positively and agree to help Turkey bolster its air defences” by approving Ankara's request to deploy Patriot missiles on the border with Syria.

“If Nato takes a positive decision to do it ... I think it would still probably be at least a matter of weeks,” the official said.