Military response to chemical weapons attack from West on table despite decision to allow inspectors in

by Martin Chulov in Beirut

Syria appears to have bowed to international pressure to allow UN investigators to travel to the scene of last week's chemical weapons attack in Damascus, allowing a forensic science team to visit the site today.

The green light for the UN inspection came almost five days after the attack and was immediately greeted with scepticism by western leaders and chemical weapons experts, who say it may now be too late for inspectors to gather useful scientific results. An American official told reporters the move was "too late to be credible".

The US, Britain and France have been warning of a "serious response" to the attack, and their rhetoric has been intensifying.

David Cameron is pushing for military action and government sources said the UK and allies were considering a range of options, including air strikes, the imposition of a no-fly zone and arming the rebels in Syria. Air strikes were seen as the most likely response.

The prime minister is understood to be pressing for a response within a week or so. Any bombardment would be direct retaliation for the use of chemical weapons and not intended as a wider intervention in the Syrian conflict. The use of ground troops – "boots on the ground", in Whitehall parlance – has been ruled out by Britain.

The foreign secretary, William Hague, said it was "clear it was the Assad regime" that had carried out the attack.

Tehran and Damascus warned yesterday against any form of western response, which Syrian state television said would turn the region into a "ball of flame".

Downplaying the significance of Syria's decision to let UN weapons inspectors visit the site of the attack, Hague said all the evidence suggested the regime was to blame and inspectors would have been admitted last week if Damascus had nothing to hide. "We cannot, in the 21st century, allow the idea that chemical weapons can be used with impunity, that people can be killed in this way and that there are no consequences for it," Hague said.

Government sources insisted that Britain would only act in a lawful way, but the government does not believe that necessarily requires a UN security council resolution. Intervention could be justified legally on humanitarian grounds or under international law relating to chemical weapons.

General Sir Nick Houghton, the chief of the defence staff, will be discussing the military options with fellow defence chiefs, including the most senior US military officer, General Martin Dempsey, chairman of the joint chiefs of staff, at a summit in Amman, Jordan today.

Russia warned the US against repeating past mistakes, saying unilateral military action in Syria would undermine efforts for peace and have a devastating impact on the security situation in the Middle East.

Hamish de Bretton-Gordon, a former commanding officer at the UK's Joint Chemical, Biological, Radiological and Nuclear Regiment, said he remained sceptical about what the UN team could achieve in such an insecure area.

"Evidence about the delivery [of the gas] will be key to determining who perpetrated this massacre," he said. "Although much of the rocketry has been moved around since it landed, it is likely to provide important clues."

Activists and residents in the three areas targeted by the attack have gathered the remnants of numerous distinctively shaped rockets which are believed to have contained the neurotoxins.

Many of the rockets are relatively intact, though their noses were buried deep in soil or bitumen, suggesting that they dispersed the chemicals above ground and did not explode on impact.

The affected areas have been bombed repeatedly over the past three days, with Syrian officials announcing they were continuing an advance into the rebel-held east of Damascus, an assault which started around the same time as residents first complained of exposure to a noxious gas.

De Bretton-Gordon said the large amount of nerve gas dropped and the tactics used pointed to Bashar al-Assad's regime being responsible. He said scientists could still be able to determine the nerve agent used.

"Realistically, only the regime has access to that amount of agent," he said. "This appears to have been a very well-planned operation, from the conventional bombardment before to break all the doors and windows to allow the gas to move freely, to the use of 20 or so rockets [to deliver the gas] and then the army following up. It is a textbook operation."

Cameron spent much of the weekend on the phone to world leaders, including Barack Obama, the Canadian prime minister, Stephen Harper, and the French president, François Hollande. A call to the German chancellor, Angela Merkel, was also scheduled.

Cameron and Hollande "agreed that a chemical weapons attack against the Syrian people on the scale that was emerging demanded a firm response from the international community", a No 10 spokesman said. "This crime must not be swept under the carpet."

Douglas Alexander, the shadow foreign secretary, said he would call for a recall of parliament to discuss the crisis. Several Conservative MPs had earlier requested such a move.

"If, in reality, the prime minister is now considering military options involving UK personnel, then of course I would expect him to seek a recall of parliament and to come to the House of Commons and make his case in advance of a decision being made," Alexander said. No 10 said it had not ruled out a recall.

The UN said Syrian officials had offered the necessary co-operation, including a cessation of hostilities in the area where the attack happened. The promise appeared to have been obtained by the high representative for disarmament affairs, Angela Kane, during meetings with senior Assad officials over the weekend.

Additional reporting by Rory Carroll

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