Russian troops have started to withdraw from Syria after yesterday’s surprise announcement by President Vladimir Putin.

The first planes left Hmeimim air base in Syria on March 15, the Russian defense ministry said.

Western officials cautiously welcomed the move, saying Russian troops withdrawal could pressure Syria’s government to engage in talks.

Peace talks aimed at resolving the conflict are entering a second day.

Meanwhile, a UN commission will present a report on war crimes in Syria later.

The Russian force reduction was announced during a meeting between Vladimir Putin and his defense and foreign ministers.

Russia is a key ally of Syrian President Bashar al-Assad, and his office sought to reject speculation there was a rift between the two countries, saying the move was mutually agreed.

The Russian air campaign started in September 2015, tipping the balance in favor of the Syrian government and allowing it to recapture territory from rebels.

No details have been given on how many planes and troops would be withdrawn from the Hmeimim base, in Latakia province, or a deadline for completing the pullout.

“The first group of Russian planes has flown out of the Hmeimim air base for their permanent bases on the territory of the Russian Federation,” the defense ministry statement said.

Russian TV earlier showed aircraft being refueled and crates being loaded with equipment.

Aircraft from the base would make the flight to Russia – more than 3,000 miles – in small groups each led by Il-76 or Tu-154 transport planes, the ministry added.

They would then go their separate ways to their own bases after crossing the Russian border, it said.

Su-24 tactical bombers, Su-25 attack fighters, Su-34 strike fighters and helicopters were returning home, the TV said.

It is not clear how many military personnel Russia has deployed, but US estimates suggest the number ranges from 3,000 to 6,000, AP reports.

Vladimir Putin, however, said Hmeimim and Russia’s Mediterranean naval base at Tartus would continue to operate as normal.

Russia had long insisted its bombing campaign only targeted terrorist groups but Western powers had complained the raids hit political opponents of President Assad.

In a statement, the Syrian government said the plan was agreed between the two countries.

Meanwhile, the UN Commission of Inquiry on Syria will present its report on war crimes committed by all sides in Syria’s war to the UN Human Rights Council on Tuesday in Geneva.

In a phone call, Vladimir Putin and Barack Obama discussed the situation in Syria and the “next steps required to fully implement the cessation of hostilities” agreed last month, the White House said.

The Kremlin said both “called for an intensification of the process for a political settlement” to the conflict.

The Russian move has received a guarded welcome from Western diplomats and the Syrian opposition.

An unnamed US official quoted by Reuters said Washington was encouraged by the Russian move, but it was too early to say what it means or what was behind it.