Cameron and Obama warn Syria over chemical weapons

In a phone call the two leaders said if President Bashar Assad made such a move it “would force them to revisit their approach so far”, Downing Street said.

The two leaders said there was “much more to do” to stop the brutal killing of civilians in the Middle East state.

Syrian regime forces shelled two central districts in the capital, Damascus, yesterday before troops backed by tanks swept through to carry out house-to-house raids, killing at least 35 suspected rebels.

The capital is one of many fronts Assad’s regime is struggling to contain as the 17-month-old rebellion is swelled by people appalled by his brutal tactics.

Government forces are also engaged in a major battle for control of the northern city of Aleppo as well as the country’s south, east and centre.

Earlier this week President Obama warned that any movement of Syria’s stockpile of chemical weapons would be a “red line” which would have “enormous consequences”.

Mr Cameron also discussed the situation with French President Francois Hollande and the two European nations agreed to “work more closely to identify how they could bolster the opposition and help a transitional government.