Syria conflict: Philip Hammond urges chemical weapons investigation
The UK defence secretary is demanding Syria allows a UN team into the country to investigate whether chemical weapons have been used.
Phillip Hammond said both the UK and US were alarmed by "limited but persuasive evidence" of their possible use.
US intelligence agencies believe nerve agent sarin may have been used in Syria - US President Barack Obama has said such an act would cross a "red line".
A UN team is on stand-by to deploy there within two days if Syria agrees.
Mr Hammond met US Defence Secretary Chuck Hagel last week.
He said both the UK and the US governments were "very keen" to establish the facts about the possible use of chemical weapons and put them before the international community, ideally in the form of the United Nations.
"No one is suggesting that chemical weapon use has taken place over two years, this is a recent set of reporting and it's causing very significant concern," Mr Hammond said.
"We demand that Assad allows in the UN team to investigate the use of chemical weapons. Once we have got the evidence we will present it to our allies and partners."
Green light absent
In March, Syria's government and opposition called for an inquiry into an alleged chemical weapon attack in Khan al-Assal in the north of Syria which killed at least 27 people, with both sides blaming each other.
Footage of alleged victims of a more recent nerve gas attack in the Sheikh Massoud district of Aleppo has surfaced online.
The 15-strong UN team is headed by a Swedish scientist, Ake Sellstrom. Two of its members are pre-positioned in Cyprus.
The UN wants to be allowed to be able to investigate all credible allegations, not just the ones the Syrian authorities allow it to see.
UN secretary-general Ban Ki-moon has urged the Syrian authorities to provide "full and unfettered" access to the team.
In the absence of a green light to enter Syria on these terms, the team has been analysing information and trying to collect what it can from outside the country.
Syrian officials have admitted to stockpiling chemical weapons, though they say they will never use them against their own people.
More than 70,000 people are estimated to have been killed since conflict erupted in Syria in March 2011.
In the most recent developments, Syria has accused Israel of launching rocket attacks on Damascus, after a night of huge explosions.
Syrian state media said the rockets hit the Jamraya research centre, which Western officials have suggested may be involved in chemical weapons research.
Speaking on the Andrew Marr show on BBC One, Mr Hammond also ruled out accelerating the withdrawal of UK troops from Afghanistan.
It comes after three British soldiers were killed when their Mastiff armoured vehicle was hit by a roadside bomb in the Nahr-e Saraj district of Helmand province on Tuesday.
Five US soldiers serving as part of the Nato force in Kandahar province were later killed by another roadside bomb and reports on Saturday said an Afghan soldier had turned his weapon on coalition troops, killing two people.
Mr Hammond said there was a "very clear drawdown plan" to end the UK's combat mission in Afghanistan at the end of next year.
"This is a planned transition of responsibility to the Afghans," he said.
"I think the schedule we've got is the right one.... I don't think it's practical or sensible to try and go any faster."
Regarding a High Court claim launched on behalf of thee Afghan interpreters for a judicial review of the government's decision not to treat them in the same way as interpreters in Iraq, who were given the right to resettle in the UK after the war, Mr Hammond told the programme there was already a mechanism in place to deal with cases where workers were at risk of harm in Afghanistan.
He said the UK had about 1,100 locally-employed civilians in Afghanistan, about half of them interpreters who were estimated to have an average of five to six dependants each.
"It is possible for people to seek settlement in the UK if they are genuinely at risk," he said.
"But we're looking to build the future of Afghanistan, we're looking to make Afghanistan a success story.
"And some of these people are well educated, capable people who ought to be able to play a part in Afghanistan's future."
He said the government was trying to put together packages that would make it attractive and practical for them to stay in Afghanistan.
"Not in Helmand because that probably wouldn't be safe," he said.
"But many of them are not from Helmand; many parts of Afghanistan are relatively peaceful."