Syria's rebels will receive an extra $60 million (£40 million) of "non-lethal" American aid, the Obama administration announced on Thursday, when an 11-nation coalition promised to "change the balance" of the conflict.
The Friends of Syria meeting in Rome promised more "political and material support" for the Syrian National Coalition, an opposition alliance fighting to overthrow President Bashar al-Assad.
William Hague, the British Foreign Secretary, will announce a new package of British assistance next week, on top of the £9.4 million already pledged.
A European Union embargo rules out the supply of weapons and America has taken a policy decision not to give the rebels any lethal equipment.
Britain is pushing for the widest possible definition of the non-lethal support that can be sent, consistent with the EU embargo. In particular, London is considering whether to provide armoured vehicles, night vision and communications equipment. "We want to do more and we want to give more types of support and we're pushing to do that," said a Foreign Office spokesman.
At Britain's insistence, the EU embargo will be reviewed in May. Hague has declined to rule out any option, including arming the rebels, explaining that policy towards Syria cannot remain "static" as the situation worsens.
Western governments fear that if they fail to provide weapons, radical Islamist groups, notably Jabhat al-Nusra, will become the strongest force in the revolt.
The new US aid, however, will be mainly humanitarian, including food and medical equipment. "No nation, no people should live in fear of their so-called leaders," said John Kerry, the new US secretary of state. He added that America's "decision to take further steps" to help the opposition was a response to the brutality of Assad's forces.
The Syrian opposition had threatened to boycott the Rome meeting because of America's failure to supply arms. Kerry's offer of fresh assistance was given a cool reception.
Washington has already provided $385 million (£257 million) in humanitarian aid and $54 million of non-lethal help to the opposition. President Barack Obama has consistently rejected advice to arm the rebels.
Sources close to the rebel Free Syrian Army (FSA) told The Daily Telegraph that yesterday's announcement from Kerry - who favoured arming the rebels when he chaired the Senate foreign relations committee - showed that the White House position was unchanged.
"They're basically saying to Kerry, 'go do a face-saving job overseas. Go and make a few announcements of new money and say you're finding ways to work with the rebels, but don't give them any clear answers'," said the source.
A report in the New York Times stating that America was helping to "train rebels at a base in the region" was misleading, added the FSA source. "If officials are talking about general training for opposition fighters, I can tell you that is not happening. They may be training a few for first-response in the event of a chemical weapons event, but the US is not training the rebels in a meaningful way."