Russia's foreign minister says Washington has asked Moscow not to target the al-Qaida's branch in Syria, the Nusra Front, for fear of hitting the moderate opposition.

Sergey Lavrov said that Russia long has insisted that the moderate, U.S.-backed opposition groups should leave the areas occupied by Nusra. He said Friday in televised remarks that Russia and the U.S. have engaged in close dialogue on how to secure a cease-fire in Syria, but added that fighting the Islamic State group and Nusra should be a top priority.

Russia first set a deadline for Syrian opposition units to withdraw from areas occupied by Nusra, but then agreed to give them more time to pull out.

Despite a Russia- and U.S.-brokered truce in Syria, fighting has continued to rage in many areas.