Syrian President Bashar Al-Assad
Syrian President Bashar Al-Assad Reuters

French authorities have launched a criminal probe of Syrian President Bashar Al-Assad's regime for alleged war crimes committed between 2011 and 2013, sources told the AFP news agency.

Paris prosecutors opened a preliminary war crimes inquiry on September 15, a source close to the case told the news agency on Tuesday. A diplomatic source confirmed the launch of the probe.

The investigation is focusing on evidence provided by a former Syrian army photographer known by the codename "Caesar," who defected and fled the country in 2013, bringing with him some 55,000 graphic photographs of scenes from the brutal conflict.

The announcement comes as the four-year war in Syria takes centre-stage at the United Nations General Assembly in New York, where President Barack Obama and his Russian counterpart Vladimir Putin have clashed over how to bring an end to the crisis.

Obama and Putin met at the General Assembly on Tuesday, breaking a year-long silence between the two.

Syria dominated the 90-minute meeting, with the two agreeing to hold talks to prevent clashing in the embattled country.

Russia has stepped up its military involvement in Syria in recent weeks, with U.S. officials accusing Moscow of sending combat aircraft, tanks and other equipment to help the Syrian army.

The United States was so concerned about reports of Russia’s increased presence in Syria that Secretary of State John Kerry phoned his Russian counterpart Sergei Lavrov a total of three times in ten days to discuss the situation.

But Obama seemed to have pledged to break the silence earlier Monday, pledging in his own UN address that he would be "willing to work with" both Russia and regional ally Iran to solve the Syria crisis. 

French President Francois Hollande has joined Obama in insisting Assad cannot play a role in the country's future, against opposition from Damascus's allies Russia and Iran.

"Russia and Iran say they want to be part of a solution," Hollande said, according to AFP.

"So we must work with these countries to explain to them that the route to a solution does not go through Bashar Al-Assad," he added.

France recently shifted its stance on Assad somewhat, saying it will not demand his departure as a precondition for peace talks.