Talks on whether Britain will launch air strikes against Islamic State (IS) are continuing as a US-Arab coalition launched air strikes against the terror group's targets in Syria.
America, along with Bahrain, Qatar, Saudi Arabia, Jordan and the United Arab Emirates, used fighter jets, bombers and Tomahawk cruise missiles fired from ships in the region.
Targets in the US-Arab strikes in Syria reportedly included the IS stronghold of Raqqa, to where British hostage Alan Henning is reported to have been moved.
Damascus said Washington informed Syria's United Nations envoy before the attacks began at about 1.30am British time.
A Ministry of Defence spokeswoman said of the action: "Our position in Iraq and Syria is the same. Discussions are ongoing, no decision has been taken to our involvement."
Britain has been helping supply arms to Kurdish peshmerga fighters taking part in the struggle with IS, as well as offering support to the new inclusive Iraqi government led by Haider Abadi in Baghdad.
It was also a driving force behind a UN Security Council presidential statement on Friday calling on the international community to help Iraq defeat the extremists.
But David Cameron has ruled out putting British "boots on the ground" and it has been unclear whether the UK will join the US and France in air strikes against Islamic State forces.
The UK Prime Minister has said he would want to consult the House of Commons, if possible, before engaging British forces, raising the prospect of a possible recall of Parliament after his return from the US on Thursday.
Mr Cameron is also to meet the president of Iran to urge him to join an international effort to tackle IS.
The meeting with Hassan Rouhani, at a crucial United Nations summit in New York, will be the first time a British prime minister has held face-to-face bilateral talks with an Iranian president since the country's Islamic revolution in 1979.
It marks the PM's determination to enlist the active support of regional powers in the Middle East in taking on IS, which has seized control of swathes of territory in Iraq and Syria and carried out a string of atrocities against local people and foreigners as it seeks to impose its own brand of extremist Sunni Islam.
Mr Cameron hopes to secure UN approval for a comprehensive strategy to deal with the brutal militant group, and will join US President Barack Obama and other members of the UN Security Council to discuss the threat posed by foreign fighters - thought to include hundreds of Britons - engaged in the conflict.
He will use an address to the UN General Assembly to call on the whole world to come together to offer broad-based support for the new inclusive Iraqi government led by Mr Abadi in Baghdad and to defeat the threat from extreme Islamist groups such as IS, also known as Isis or Isil.
Shadow business secretary Chuka Umunna said it was "inconceivable" that Mr Cameron could commit UK forces to air strikes without seeking the approval of MPs and said Labour would apply the same criteria as to last year's planned strikes on Syria - which the Opposition succeeded in voting down - to any new proposal.
He told Sky News: "Isis need to be eliminated. What they are doing in the region is evil, is terrible.
"Obviously the Prime Minister hasn't determined yet that the UK should get involved.
"If that is something he does, the Labour Party will apply the same criteria to whether or not we choose to support the intervention as we applied to the proposed Syrian action last year - is there a legal basis to intervene, is there a plan for intervention, and, importantly as well, learning the lessons from Iraq, is there a plan for what happens after?
"It is inconceivable that the Prime Minister could press on with air strikes frankly without consulting Parliament and seeking proper consultation with Parliament."