Two separate reports, one French and the other Israeli, are claiming that Jordanian, Israeli and American commandos are leading hundreds of Syrian rebels they have trained in a push on Damascus.

The reports claim a force of some 300 men crossed into Syria from Jordan on August 17, with a second group crossing on the 19th. The advance has been felt as far as Ghouta and, say some, may add legitimacy to claims the Syrian regime used gas in an attack on the rebel-held eastern suburb of Damascus on Wednesday.

President Bashar al-Assad has always denied using gas in the past, but equally always warned it would be used if “foreign invaders” joined the rebels and threatened the capital. He has denied bombing the suburb with nerve gas.

Analysts say this is stage one of the US strategy, training and leading in the field handpicked members of the Free Syrian Army to carve out a southern buffer zone along the Jordanian and Israeli border within which rebel forces can be trained and based.

Russia announced on Friday that it has urged the Syrian government to allow UN experts to carry out investigations into the allegations of chemical weapons use. Russia has been a key international ally of Assad and recently suggested that the chemical attack could have been orchestrated by rebels to pin blame on the government.

China also commented on the chemical investigation, saying that neither side should “pre-judge” the outcome before results of an investigation are established. “The U.N. inspection team has already gone to Syria to start their probe, and China hopes and believes they can fully consult with the Syrian government to ensure the smooth progress of the investigation work,” China’s Foreign Ministry said.

Speaking to CNN US President Barrack Obama called the events in Syria a “big event” and told reporters he did not expect cooperation with Assad’s government, based on previous experiences.

Last year Obama said that if the Assad regime crossed the “red line”, he would have to rethink his position on Syria. Quizzed on Friday about whether the latest allegations of chemical weapons use constituted ‘crossing the line’, Obama replied that the US would have to look into it further.