European countries including Britain are to review the arms embargo in Syria as part of continuing efforts to support the opposition to President Assad, David Cameron told the Commons today.
The Prime Minister told MPs last week's gathering of European leaders had agreed there was a "moral imperative" for action in Syria, which has seen bloody fighting for more than a year.
Mr Cameron said Britain was leading the way among international efforts as the second-largest donor to humanitarian aid.
And reporting on the European Council in a statement to MPs, Mr Cameron said: "A humanitarian crisis is unfolding in Syria on our watch, with over 40,000 dead and millions in need of urgent assistance as a hard winter approaches.
"We continue to encourage political transition from the top and to support the opposition which is attempting to force a transition from below.
"This should include and will include looking at the arms embargo. We must now explore all options to support the opposition to enable greater support for the protection of civilians."
Mr Cameron said there was also a strategic imperative to act because of a "growing cohort of al Qaida-linked extremists" in the country meaning there was a growing risk of regional instability.
He said: "We cannot go on as we are. Assad's regime is illegitimate, the council committed to work for a future for Syria that is democratic and inclusive with full support for human rights and minorities."
Answering Labour leader Ed Miliband, Mr Cameron added: "It is right to look at amending the arms embargo; of course, we will be keeping the arms embargo on the regime.
"There are arguments on both sides of the debate but it is a debate that should be had, that European foreign ministers will be having.
"My concern is that if we, with others, aren't helping to shape and work with the opposition, it's much more difficult to get the transition we all want to see to a peaceful, democratic Syria that respects the rights of minorities."
Responding to the statement, Mr Miliband said: "The international community must work together to end the atrocities immediately and speak with one voice in favour of a transition to a new government.
"You mentioned the arms embargo while also noting Syria is attracting a new cohort of al Qaida-linked extremists. In that context, can you go further and tell us if you are actively urging the EU to end its arms embargo or merely amending its terms?
"Do you recognise, notwithstanding the deep concern in the international community about the situation in Syria, some of the dangers in this approach, in putting weapons into a zone in which there is already deep conflict?"
Mr Cameron warned MPs that al Qaida-linked terrorists were operating in Syria as the country fragmented.
He said: "The elements that are linked to al Qaida are linked to elements of the opposition and there is very strong evidence that groups ... take an unacceptable view about Islamic extremism.
"There are very real concerns about this issue and this leads to the argument about how involved we should get with the Syrian opposition.
"There is a strong argument for saying that by being more involved with other like-minded allies, we would be able to try and support those elements of the opposition that most want to see a free and democratic and inclusive Syria."
In exchanges on Mr Cameron's statement in the House of Lords, Independent Labour peer Lord Stoddart of Swindon criticised the possible lifting of the arms embargo.
He said: "Arms mean more death. Will not the Government embark on a peace process rather than a war process and the support of some elements in Syria that are nasty and vicious and should not be supported?"
Leader of the House Lord Strathclyde, who had repeated Mr Cameron's statement, said it would be "premature" to lift the embargo but it was "right to keep it under review".
Labour former foreign secretary Jack Straw said the Government needed to engage Russia to stop the conflict in Syria.
He said: "Could you say what further efforts are being made with the Russians to try and secure some international agreement, however difficult this may be, given that Russia's compliance and consent is crucial to some overall settlement?"
Mr Cameron said if there was to be a change in government in Syria "from the top", the Russians needed to be part of the process. He added: "The Foreign Secretary (William Hague) has met and spoken to them regularly. I have discussed this issue with President Putin.
"There was a report on Thursday whilst we were in the European Council that the Russian Deputy Foreign Minister had made some interesting remarks about Syria so we will read those with care.
"Clearly everything we can do at the UN and with countries like Russia is worthwhile."