US-led coalition forces 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, 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 (SAC), 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 5,000 fighters, said a Baghdad-based spokesman, after heavy criticism of Washington's previous programme to train moderate rebels.
The Pentagon had to scrap a $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.
- Regime troops gain ground -
On the ground, regime forces gained ground in the central province of Hama backed by Russian air power, advancing on the strategic Sahl al-Ghab plain in the heaviest fighting this month.
Syria's army command said regime forces had captured Kafr Nabuda village in Hama, extending their advance around the key Damascus-Aleppo highway, while the Syrian Observatory for Human Rights said they had captured Mansoura village in the Sahl al-Ghab plain.
"The clashes are the fiercest since the Russian air campaign began on September 30," said the chief of the Britain-based monitoring group Rami Abdel Rahman, adding that dozens of Russian air strikes hit Sahl al-Ghab on Monday.
Sahl al-Ghab lies at the intersection of the provinces of Hama, Latakia and Idlib -- controlled by the powerful Army of Conquest rebel alliance, which includes Al-Qaeda affiliate Al-Nusra Front -- and has been a major target for Russian strikes.
Moscow said its air force had hit 53 targets in Syria in the past 24 hours in four provinces -- Hama, Homs, Latakia and Idlib -- which had severely disrupted IS supply chains.
Signup to our newsletter and follow us on Facebook and Twitter!
Syria's army command also reported advances in northern Latakia province, the coastal stronghold of the regime, and said regime forces had taken control of a zone outside Aleppo in the north.
As fighting intensified, the UN peace envoy to Syria, Staffan de Mistura, said he would head to Moscow then Washington to push his initiative for a political settlement to end the Syrian conflict.
He has proposed creating contact groups in addition to four working groups composed of Syrian opposition and government representatives.
The envoy has refused to reveal their makeup, but said Russia and the United States would account for the "nucleus" of the outside contact group, which could also feature Saudi Arabia, Iran and Turkey.
- 'Thirsty for destruction' -
As they demanded Moscow stop targeting non-jihadist rebels, the EU foreign ministers also said lasting peace in Syria was impossible without a transition from Assad's rule.
"The recent Russian military attacks that go beyond Daesh (IS) and other UN-designated terrorist groups, as well as on the moderate opposition, are of deep concern and must cease immediately," the 28 ministers said in a statement.
"There cannot be a lasting peace in Syria under the present leadership."
More than 240,000 people have been killed in the conflict and upwards of four million Syrians have become refugees.
French Prime Minister Manuel Valls on Monday told soldiers at a Jordanian airbase from where French fighter planes have been bombing IS that the campaign against the jihadists would take time.
"Faced with the enemies of freedom, faced with barbarity, with hordes thirsty for destruction, with torture, with degradation of humanity, we must give the strongest response," he said.
In Baghdad, security services said they were checking reports that IS chief Abu Bakr al-Baghdadi had been wounded in an Iraqi air strike on his convoy as it was heading to an IS leadership meeting.
Such claims have been made in the past and never verified, and the reports were met with mockery by pro-IS social media accounts.