The Turkish offensive against U.S.-allied Kurdish forces in the northeast of Syria opens one of the biggest new fronts in years in an eight-year-old civil war that has drawn in global powers.

Russian President Vladimir Putin warned on Friday that Islamic State militants held in northeast Syria could escape as a result of a Turkish military operation there, Interfax reported.

Russia emerged a leading power broker in Syria after it launched a military intervention there in 2015, turning the tide of the war in favor of its ally in Damascus, President Bashar al-Assad.

"There are zones located in the north of Syria where Islamic State militants are concentrated. They were guarded until now by Kurdish armed forces. Now the Turkish army is going in, the Kurds are abandoning these camps. They could just escape," Putin was quoted as saying.

"I'm not sure if the Turkish army can rapidly get this under control," Putin said, speaking during a visit to Turkmenistan.