US-led coalition forces have parachuted in ammunition to rebels in Syria, stepping up their support for groups battling jihadists as regime troops fought their fiercest clashes in weeks, aided by Russian air strikes.
Moscow entered Syria's multi-faceted civil war last month, when it began air strikes against Islamic State jihadists and other "terrorists" fighting against the regime of its ally President Bashar al-Assad.
Washington and Europe, however, accuse Moscow of targeting "moderate" groups that oppose the Syrian leader, rather than IS, and say ousting Assad is key to ending the bloody four-year conflict.
On Monday (local time), EU foreign ministers demanded Russia stop targeting non-jihadist rebels while the UN's peace envoy to Syria said he was heading to Moscow to promote a political end to the conflict.
Their calls come as the US-led coalition said it had airdropped ammunition to the Syrian Arab Coalition, which has been fighting IS militants near their northern stronghold of Raqqa for months.
US forces have carefully vetted the leader of the group, which includes up to 5000 fighters, said a Baghdad-based spokesman, after heavy criticism of Washington's previous program to train moderate rebels.
The Pentagon had to scrap a US$500 million scheme to equip and instruct thousands of Syrian rebels in Turkey and Jordan after many failed the screening process and one group gave weapons to an al-Qaeda affiliate.
"Coalition forces conducted an airdrop Sunday in northern Syria to resupply local counter-ISIL ground forces as they conduct operations against ISIL," US Central Command spokesman Colonel Patrick Ryder said, using an alternative acronym for IS.
Speaking on condition of anonymity, a US official told AFP the drop included 50 tonnes of ammunition.
A US-led coalition has for the past year carried out air strikes on IS, which controls swathes of both Syria and neighbouring Iraq.