Syria: PM says end of arms embargo sends 'clear signal' to Assad
David Cameron has said no decision has been taken on whether the UK will send arms to opposition forces in Syria.
The prime minister told MPs that the end of EU arms embargo last month gave the UK greater flexibility to respond to an ever-deteriorating situation.
The move was a "clear signal" the Syrian government could not continue to act with impunity or seek to "buy time" ahead of planned peace talks in Geneva.
Labour said there was a risk of "further escalation" in Syria.
MPs from all parties have warned that arming opposition forces could increase bloodshed in the country and lead to weapons falling into the hands of terrorists.
The UK and other EU nations have stressed their efforts are still focused on a negotiated settlement to the violence in Syria and diplomatic efforts to bring that about.
Updating MPs on the situation, the prime minister said that 80,000 people had been killed in the two-year conflict while five million people had been made homeless.
"This is not just a tragedy for Syria," he said. "This could end up being a tragedy for us too if we do not handle it properly."
Mr Cameron said the arms embargo had been counter-productive as it had not stopped extremist groups from getting hold of arms or Russia from supplying weapons to the government of President Assad.
If the international community did not act to increase pressure on the government, Mr Cameron said it would further weaken the opposition Syrian National Coalition, which supported democracy and human rights and deserved international backing.
President Assad, he added, was more likely to agree to a political transition if he thought he was losing the military initiative and "tipping the military balance" could lead to a change of approach in Damascus.
The prime minister said no decision had been taken on the supply of arms and said that the UK would only go down such a route in conjunction with allies and if clear safeguards were put in place.
"We have not made a decision..That would be a separate decision but lifting the arms embargo was the right thing to do."
Labour leader Ed Miliband said the UK's primary responsibility should be to reduce violence in Syria.
Former Lib Dem leader Sir Menzies Campbell said he was unconvinced that arming the opposition would make any difference in the face of Russia's "uninhibited and unconditional" support for the Assad government.