RUSSIA has warned Britain and America that they will be in "grave violation of international law" if they carry out airstrikes against the Syrian regime without UN approval.
Amid growing concern at home and abroad about the legitimacy and wisdom of the UK participating in a unilateral attack on the Assad regime, the Government's most senior law officer will be asked to justify Britain's participation in strikes at a meeting of the National Security Council tomorrow.
Vladimir Putin, the Russian President, spoke to David Cameron for 20 minutes tonight in a call which Downing Street described as "business-like".
He reportedly told the Prime Minister that UN weapons inspectors should be given time to analyse properly the cause of the attack. But he did not repeat comments made earlier by the Russian Foreign Minister that any unilateral action would be illegal.
But last night there were no signs of Downing Street backing away from its intention to join America in the use of military force. One source at No 10 said they still expected action within two weeks, while a spokesman for the Deputy Prime Minister, Nick Clegg, said he was also fully behind a "proportionate" response to President's Assad's use of chemical weapons.
In the US, a senior Senator warned that a military strike against Syria was "imminent" in the wake of the purported use of chemical weapons by the regime in Damascus, while the US Secretary of Defence, Chuck Hagel, indicated the US was not willing to act alone or outside the "framework of a legal justification".
As he mulls his options, President Barack Obama is likely at least to await the results of the mission by United Nations inspectors to the site where the armaments allegedly landed last Wednesday.
But Senator Bob Corker, the most senior Republican on the Senate Foreign Relations Committee, suggested Mr Obama had already made up his mind to act. "I think a response is imminent," he told CBS. "I don't think there's any question in the administration's mind that chemical warfare has been used and that when we're involved, it's surgical, proportional to what has occurred."
Mr Cameron will return to Downing Street from his holiday in Cornwall on Tuesday morning and is expected to make a decision on whether to recall Parliament. The move is seen as increasingly likely after a succession of Tory MPs made clear to Downing Street they expected to be consulted ahead of any action.
The Conservative MP Sarah Wollaston said there was no threat to UK national security and Parliament should be consulted to act as a brake on an escalation of the situation. "I sense that we are on a headlong rush into escalating this conflict and I think Parliament can act as a natural brake to that," she said.
Without a UN mandate for action - which would be impossible to achieve because of Russian and Chinese opposition - the legal mandate for war would likely rest either on the "right to protect" civilians, as happened when Nato bombarded Serbia in 1999, or the need to prevent breaches of international conventions outlawing the use of chemical weapons.
The Independent understands that the Attorney General, Dominic Grieve, has been asked by Mr Cameron to review the legal situation and report to the NSC at its meeting tomorrow.
However, the Foreign Secretary William Hague appeared to suggest that the Government did not see any significant legal obstacles to action. He told the BBC: "The United Nations Security Council has not shouldered its responsibilities on Syria otherwise there would have been a better chance of bringing this conflict to an end a long time ago.
"So, is it possible to act on chemical weapons, is it possible to respond to chemical weapons without complete unity on the UN Security Council? I would argue, yes it is. Otherwise, of course, it might be impossible to respond to such outrages, such crimes and I don't think that is an acceptable situation.
"It is possible to take action based on great humanitarian need and humanitarian distress, it's possible to do that under many different scenarios. But anything we propose to do on this, the strong response that we've talked about, whatever form that takes, will be in accordance with international law."y."