Syrian rebels could be armed by the UK in a fresh push to oust President Bashar Assad and end the bloodshed after David Cameron ordered officials to re-examine all options.
A Downing Street official said the Prime Minister wanted to put previously rejected measures "back on the table" amid frustration at the failure to halt the 20-month conflict.
Mr Cameron had vowed to redouble his efforts after visiting a refugee camp in Jordan and hearing "horrendous" stories of some of those who have fled the violence.
British diplomats are already set for talks with opposition military commanders as part of the renewed drive - which the premier said should be a top priority for newly-re-elected US president Barack Obama.
He insisted during a three-day Middle East tour that Britain has no plans at present to directly arm rebel forces, pointing out that it was prohibited under the terms of a European Union arms embargo.
Whitehall officials are said however to be considering whether it could be justified under United Nations resolutions and sounding out potential support within Europe for amending the current restrictions.
Other possibile new approaches are the creation of United Nations-enforced "safe zones" within Syria's own borders for refugees - a move being urged on the UN by neighbouring Turkey.
A No 10 official said: 'We're 20 months into this and there is a sense of frustration that we haven't been able to bring an end to the violence.
"The Prime Minister wants to come back and look at things that were on the table a year ago which we didn't want to do then. He wants to put them back on the table.
'We haven't ruled anything in and we haven't ruled anything out. This is the moment to get some impetus going forward. We want to put everything on the table."