French President Francois Hollande has called on Europe's leaders to lift an arms embargo on Syria to help groups fighting the regime of President Bashar al-Assad.
The issue is expected to be discussed on Friday at the second and final day of an EU summit in Brussels.
"Political solutions have now failed [in Syria], despite every pressure," Hollande said on Thursday.
"We must go further because for two years there has been a clear willingness by Bashar al-Assad to use every means to hit at his own people."
London and Paris had earlier announced they were seeking to lift the EU embargo to enable them to deliver weapons to Syrian rebels.
"Our goal is to convince our partners at the end of May, and if possible before.... If by chance there is a blockage by one or two countries, then France will take its responsibilities," Hollande said.
A British official said current European efforts were failing and a change in tactics was needed to alter the balance on the ground and influence Assad.
But a number of EU countries have been sceptical about dropping the arms ban.
German Chancellor Angela Merkel said the EU needed to "proceed very cautiously" on lifting the embargo.
Austrian Chancellor Werner Faymann said his country was not prepared to lift the ban.
"We are against the end of the arms embargo. We think the delivery of arms does not contribute to a possible solution," he told reporters as talks began on Friday.
The British-French announcement angered Damascus but drew a guarded welcome from the opposition.
Opposition activists called on the two governments to provide heavy weaponry, not just small arms, to tilt the balance in the two-year uprising against Assad's rule.
Assad's government, like its key foreign ally Russia, said any such arms shipments would be a "flagrant violation" of international law.
Laurent Fabius, the French foreign minister, told France Info radio that Britain and France will ask "the Europeans now to lift the embargo so that the resistance fighters have the possibility of defending themselves".
Fabius said Assad's government was receiving weapons from Iran and Russia which gave it an edge over the opposition.
He said Paris and London would press for quick new EU talks on the Syria arms embargo, which was extended on February 28 for three months by EU foreign ministers, although such sanctions are always reviewed in case events change.
Fabius said the two governments were ready to go ahead with arms deliveries even without the support of their partners.