The Russian defense minister proposed on Friday that Russia and the U.S.-led coalition launch joint action against al-Qaida’s branch in Syria, known as the Nusra Front.

A spokesman for the U.S. State Department said no agreement on such action has been made with Russia.

Defense Minister Sergei Shoigu said that Moscow had proposed to Washington that the coalition call on all factions eager to abide by a cease-fire in Syria to leave the areas where the al-Qaida branch is active by May 25. Then Russia and the U.S.-led coalition could conduct joint strikes against the Nusra Front and any other groups refusing to honor the truce, Shoigu suggested.

State Department spokesman John Kirby said “there is no agreement to conduct joint airstrikes with the Russians in Syria” but added Washington and Moscow are discussing “proposals for a sustainable mechanism to better monitor and enforce the cessation of hostilities.”

Earlier, Pentagon spokesman Navy Capt. Jeff Davis would not comment directly on the proposal, which he said has not been formally presented to the United States. But he said the U.S. military is not cooperating or collaborating on operations with Russia in Syria except to maintain airspace safety.

“Russian operations are supporting the Assad regime and our focus is solely on degrading and defeating ISIL,” he said, using an alternative acronym for the Islamic State.

Shoigu warned that Moscow reserves the right to unilaterally strike militants refusing to respect the cease-fire, as well as weapons and militants crossing into Syria from Turkey, starting from May 25.

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