AP — The Pentagon says Russia will bear responsibility for the resulting humanitarian crisis in Syria if the Moscow-backed Syrian military attacks the northern city of Idlib.

Eric Pahon, a Pentagon spokesman, says the U.S. and its allies are concerned about the deadly consequences if Syrian President Bashar Assad, with support from Russia and Iran, launches an offensive against Idlib, the last major rebel stronghold in Syria. Government forces have been massing troops near the city, and Russia and Syria have launched airstrikes on Idlib for weeks.

Pahon says the U.S. questions the continued presence of more than a dozen Russian warships in the Mediterranean Sea near Syria. He says the ships must operate safely and abide by international law.

Turkey has called for a cease-fire, but Russia and Iran rejected the plan.