A fighter from the Free Syrian Army’s Al Rahman legion carries a weapon as he walks towards his position on the front line against the forces of Syria’s President Bashar al-Assad in Jobar, a suburb of Damascus.

U.S. forces have carried out an air drop of small arms ammunition to Syrian Arab rebels in northern Syria, barely two weeks after Russia raised the stakes by intervening in the war on the side of President Bashar al-Assad.

A U.S. military official, speaking on condition of anonymity, said on Monday the air drop of supplies to the opposition fighters on Sunday was part of a revamped U.S. strategy announced last week to help rebels in Syria battling ISIS militants.

Last week, Washington shelved a program to train and equip “moderate” rebels opposed to Assad who would join the fight against ISIS.

The only group on the ground to have success against ISIS while cooperating with the U.S.-led coalition is a Kurdish militia, the YPG, which has carved out an autonomous zone in northern Syria and advanced deep into ISIS’s stronghold Raqqa province.

On Monday, the YPG announced a new alliance with small groups of Arab fighters, which could help deflect criticism that it fights only on behalf of Kurds. Washington has indicated that it could direct funding and weapons to Arab commanders on the ground who cooperate with the YPG.

Syrian Arab rebels said they had been told by Washington that new weapons were on their way to help them launch a joint offensive with their Kurdish allies on the city of Raqqa, the de facto ISIS capital.

The Russian intervention in Syria has wrongfooted the U.S. administration of President Barack Obama, which has been trying to defeat ISIS while still calling for Assad’s downfall.

U.N. pushes Russia, U.S. on Syria

Meanwhile, the U.N. mediator trying to convene Syria peace talks said on Monday it was urgent for Russia and the United States to reach an understanding to avert a military escalation that could effectively dismember the country.

The two powers are pivotal to ushering Syria’s warring sides into talks, Staffan de Mistura said, though their differences seem so deep Moscow and Washington may not be able to establish a cohesive steering group of countries with peacemaking clout.

He said he would hold talks in Russia on Tuesday and then in Washington. De Mistura said intensifying fighting coinciding with Russia’s military intervention in Syria made it more urgent to get Syrian government and opposition groups talking.

“What we must all avoid at all cost at this stage … is a continuation of conflict… and a partition which de facto is already being seen as a possibility – and we consider that a tragedy,” he told a news conference in Geneva.

“At the same time the situation could move into a toxic type of cocktail, a combination of a creeping Afghanistan with shades of Libya and Somalia. Hence the need for an urgent political process to start now.”

Russia’s entry into the civil war on Syrian President Bashar al-Assad’s side had “introduced new dynamics into the situation” and quickly displaced 40,000 civilians, Mistura said, and more could flee if they feared intensified fighting.

“I am going to Washington immediately after Moscow – after all it makes sense since the two countries have been discussing, and need to discuss the future steps,” he said.

De Mistura said Assad’s government had signalled its readiness to join four working groups that he planned to convene in Geneva to tackle aspects of post-conflict Syria. But the opposition Syrian Opposition Coalition has said it would not attend because of Russia’s heavy air strikes on rebels.

The U.N. plan is for the talks to be supported by a contact group of interested countries that de Mistura said would include the United States, Russia, Saudi Arabia, Iran, Turkey and other regional players.

“If some countries don’t want to talk to each other, one could imagine separate contact groups that then are facilitated to discuss through the help of the U.N.,” he said.

He urged Damascus to end its barrel-bombing campaign against rebels and said its forces and the Russian military must respect a stalled, regional U.N.-brokered ceasefire deal that would allow evacuations of civilians and wounded from the town of Zabadani and villages of Kufreya and al-Foua.

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