Syria crisis: Diplomacy has not worked, says William Hague
Diplomatic pressure on Syria has failed and the UK is considering its response to a suspected chemical attack, Foreign Secretary William Hague says.
He told the BBC it would be possible for the UK and its allies to respond without the UN's unanimous backing.
In Syria, UN inspectors visited the site of the suspected attack after their convoy was shot at by snipers.
The PM is cutting his holiday short and is expected to hold a National Security Council meeting on Wednesday.
Deputy Prime Minister Nick Clegg has also cancelled a visit to Afghanistan to meet British troops.
Downing Street said a decision on whether to recall Parliament would be made on Tuesday.
The suspected chemical attack took place on Wednesday near the Syrian capital Damascus, and reportedly killed more than 300 people.
Weapons inspectors carried out tests at the scene on Monday after unidentified snipers shot at one of their vehicles, a UN spokesman said.
Mr Hague told BBC Radio 4's Today programme while he could not go into options or a timetable for action, he was not "going to rule anything in or out".
"We, the United States, many other countries including France, are clear that we can't allow the idea in the 21st century that chemical weapons can be used with impunity," he said.
A Downing Street spokesman said Prime Minister David Cameron had called Russia's President Vladimir Putin on Monday afternoon to discuss Syria and that they had reiterated the position that the use of chemical weapons should merit a "serious response" from the international community.
But while Mr Cameron "made clear there was little doubt" the attack was carried out by the Syrian regime, Mr Putin "said they did not have evidence of whether a chemical weapons attack had taken place or who was responsible," the spokesman said.
MPs are due to return to the Commons on 2 September but there have been demands for Parliament to be recalled.
Labour's shadow foreign secretary Douglas Alexander said he would "expect the prime minister to make his case to Parliament" before a decision was made about UK involvement.
The prime minister also had phone calls with other leaders, including US President Barack Obama, this weekend, where they agreed on the need to take "strong action".
He will return several days early from his holiday in Cornwall with his family so he can chair Wednesday's high-level security briefing of senior ministers and defence and intelligence chiefs.
It is understood the most likely military response would be a one-off or limited guided missile strikes on Syrian military targets fired from US Navy warships, says BBC security correspondent Frank Gardner.
Prof Michael Clarke, of the Royal United Services Institute, said: "Military advice to politicians in the US and the UK is 'don't think you can dabble in this - you have to go in with both feet'".
He told the BBC's PM programme limited air strikes might inconvenience the regime but were no guarantee you could stop it.
Other options - such as a no-fly zone or a safe haven - would have to be led by the US, and at the moment most of the "sabre-rattling" was coming from France and the UK - not the US, he added.
Whitehall officials have told the BBC the next key decisions would probably be taken at Wednesday's National Security Council meeting.
Mr Hague said diplomatic methods to resolve the civil war in Syria had "failed so far".
He said the UN Security Council, split over Syria, had not "shouldered its responsibilities".
The council is made up of 15 members including permanent members China, Russia, France, the US and the UK which have the power to veto any resolution.
But any action could be taken "without complete unity on the UN Security Council", he said.
He said a response could be "based on great humanitarian need and distress" and "in accordance with international law".
The foreign secretary said the suspected chemical attack was carried out by Syrian President Bashar al-Assad's regime but it blames rebel forces saying footage of the attack was "fabricated".
- 01:15: 21 August (10:15 GMT 20 Aug): Facebook pages of Syrian opposition report heavy fighting in rebel-held eastern districts of the Ghouta, the agricultural belt around Damascus
- 02:45: Opposition posts Facebook report of "chemical shelling" in Ein Tarma area of the Ghouta
- 02:47: Second opposition report says chemical weapons used in Zamalka area of the Ghouta
- Unverified video footage shows people being treated on pavements in the dark and in a makeshift hospital
- Reports say chemical weapons were used in Ghouta towns of Irbin, Jobar, Zamalka and Ein Tarma as well as in Muadhamiya to the west, but this is not confirmed
- Syrian government acknowledges military offensive in the Ghouta but denies chemical weapons use