The United States encouraged its Syrian Kurdish allies to reach Monday's landmark deal with the Islamist-led government in Damascus, six sources said, an agreement that could stave off further conflict in northern Syria at a time of uncertainty over the future of U.S. forces deployed there.

The deal aims to stitch back together a country fractured by 14 years of war, paving the way for Kurdish-led forces which hold a quarter of Syria to merge with Damascus, along with regional Kurdish governing bodies. Key details of how this will happen have yet to be spelt out, however.

General Mazloum Abdi, head of the Kurdish-led Syrian Democratic Forces (SDF), was flown to Damascus for Monday's signing with interim President Ahmed al-Sharaa aboard a U.S. military aircraft, three sources said.

Three other sources - U.S. officials - said the United States had encouraged the SDF to move towards an agreement to resolve its status in the new Syria - the focus of multi-track talks which began after Bashar al-Assad was toppled in December and which Reuters reported on in January.

"The U.S. played a very crucial role," a senior regional intelligence source said.

The deal came at a moment of pressure on both sides.

Sharaa is grappling with the fallout of sectarian killings which were reportedly carried out by militants aligned with his government, while the SDF is locked in conflict with Turkey-backed Syrian groups who are allied to Damascus.

Four sources, including one close to the Syrian government, said the sectarian violence had nudged along the agreement.

The intelligence source and a Damascus-based diplomat expected the deal to ease Turkish military pressure on the SDF, deemed by Ankara as an extension of the outlawed Kurdistan Workers Party (PKK). Turkey has welcomed the agreement.

A Syrian government official said the presidency would work to address pending issues between the SDF and Turkey.

DEEP TIES

Washington has developed deep ties to Syria's Kurdish groups since deploying forces to the country to fight Islamic State a decade ago, partnering with Kurdish fighters despite objections from Turkey.

The U.S. troop deployment has come into renewed focus since President Donald Trump returned to power.

Ahead of any policy decisions on Syria, the Pentagon has started developing plans for a potential withdrawal, should one be ordered, U.S. officials tell Reuters.

Still, a U.S. defense official told Reuters on Tuesday there was no sign that a pullout was imminent.

The U.S. defense official said General Michael Kurilla, commander of U.S. Central Command, had helped pushed the SDF towards the deal but that the agreement was already moving along.

The thinking in the U.S. administration was that the SDF would be unlikely to hold onto its territory in the long-term if it faced pressure from Turkey and the new Syrian government combined, the U.S. defense official said.

"The United States is looking for ways to withdraw from Syria without chaos and blowback. The best way of doing that is to secure a deal among the Syrian factions," said Aron Lund of Century International, a U.S.-based think tank.

"A negotiated handover makes sense for the United States. It's Washington's best bet, to avoid conflict between the Kurdish-led forces and the new government in Damascus, and to prevent a Turkish attack across the border," he said.