The U.S. and Russia vowed Monday to step up efforts to convince warring parties in Syria to abide by a troubled cease-fire agreement struck in February.

“We have decided to reconfirm our commitment to the (cease-fire) in Syria and to intensify efforts to ensure its nation-wide implementation,” the two powers said in a joint statement.

Russian Foreign Minister Sergei Lavrov told U.S. Secretary of State John Kerry during a phone call Monday that measures must be taken to stop “extremists” in Syria being supplied via Turkish territory, the Russian foreign ministry said.

Lavrov and Kerry stressed the need for the Syrian government to continue talks with the whole spectrum of the opposition, the foreign ministry said, adding the phone call took place on the initiative of the United States.

Reuters