No options are off the table if Syria's ruling regime refuses to seriously engage in an international conference to broker peace in the country, Foreign Secretary William Hague said today.
Mr Hague said the conference between President Bashar Assad's regime and Syrian opposition leaders should be held as soon as possible, telling MPs it must be focused on agreeing a full transitional body to take over running the country.
He told the House of Commons that if the the regime did not engage seriously, the international community would have to look at other options.
Mr Hague said the case for the EU to amend its arms embargo, which would allow the international community to arm the rebels, was "compelling".
The Foreign Secretary said: "We have to be open to every way of strengthening moderates and saving lives rather than the current trajectory of extremism and murder.
"We have not sent arms to any side during the conflict of the Arab Spring. No decision has been made to go down this route and if we were to pursue this, it would be under the following conditions - in co-ordination with other nations, in carefully controlled circumstances and in accordance with our obligations under national and international law.
"The United Kingdom and France are strongly of the view that changes to the embargo are not separate from the diplomatic work but essential to it. We must make clear that if the regime does not negotiate seriously at the Geneva conference, no option is off the table.
"There remains a serious risk that the Assad regime will not negotiate seriously. This is the lesson of the last two years in which the regime has shown that it is prepared to countenance any level of loss of life in Syria for as long as it hopes it can win militarily.
"We also have to persuade the opposition to come to the table, recognising how difficult it is for them to enter in to negotiations with a regime that is butchering thousands of people."
Mr Hague added: "All our efforts are directed at ensuring the coming conference in Geneva has the greatest possible chance of success.
"We are entering in the coming weeks in to a period of the most diplomacy yet - to bring together permanent members of the UN Security Council, to attempt to create real negotiations and to open up the possibility of a political solution.
"The Prime Minister is fully committed personally to these efforts and the central role of the Foreign Office over the coming weeks will be to support this process. At the same time, our work to save lives, to stabilise neighbouring countries and to support the national coalition inside Syria will continue to be stepped up.
"With every week that passes, we are coming closer to the collapse of Syria and a regional catastrophe, with the lives of tens of thousands more Syrians at stake. We are determined to make every effort to end the carnage, to minimise the risk to the region and to protect the security of the United Kingdom."
Mr Hague said there was now physiological evidence from inside Syria that the nerve agent Sarin had been used.
He added: "There is a growing body of limited but persuasive information showing that the regime used, and continued to use, chemical weapons.
"We have physiological samples from inside Syria which have shown the use of Sarin, although it does not indicate the scale of that use. Our assessment is that chemical weapons use in Syria is very likely to have been by the regime. We have no evidence to date of opposition use.
"We welcome the UN investigation, which in our view must cover all credible allegations and have access to all relevant sites in Syria."