French President Francois Hollande said on Thursday that the situation in Syria was still too unsure to start supplying weapons to opposition rebels, an idea France backs in the longer term.
France and Britain are both pressing for the relaxation of an arms embargo on Syria so that arms can flow to outgunned rebels waging a two-year-old uprising against Syrian President Bashar al-Assad.
The embargo expires on June 1 and both countries say it should be allowed to lapse. But Hollande said that before arms were delivered to Syria, guarantees were needed they would not fall into the hands of Islamist fighters.
"We will not do it as long as we cannot be certain that there is complete control of the situation by the opposition," Hollande said during an interview on France 2 television.
A Cairo-based coalition of opposition groups in exile named the Syrian National Council is recognised by many countries, including the entire Arab League, as the sole legitimate representative for rebels fighting Assad's government forces.
But the group has suffered internal divisions and is said to have only limited control over rebels on the ground in Syria. Islamist groups including the al Qaeda-linked Nusra Front have been gaining ground at their expense.
Western countries are concerned that delivering weapons to Syria will backfire if the Nusra Front captures them and gains a military edge over other rebel factions.
However, the Free Syrian Army recognised by foreign powers is sorely lacking means to fight back against Assad's warplanes, and has warned it could lose ground unless allies provide anti-aircraft guns and other equipment.
Both France and Britain tried in vain to convince other EU leaders to relax the embargo at a European Council meeting last week, and EU foreign ministers are expected to discuss the issue further this weekend.