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.
On Wednesday, Cameron 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.
Arming rebels is one method being considered in new efforts to end the war
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 the 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.
However, Whitehall officials are said to be considering whether it could be justified under United Nations resolutions and sounding out potential support within Europe for amending the current restrictions.
Fighting has raged in the country for almost two years
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.
Downing Street later confirmed that while there were no plans for Britain to arm the rebels, officials were not ruling out any options for the future.
"We are frustrated by what is happening in Syria, we are frustrated by the fact that the regime is still in place and has not stopped the killing," the prime minister's spokesman said.
"We should not be ruling out options for the future."