LONDON -- Secretary of State John Kerry said yesterday that Russia's movement of tactical aircraft and surface-to-air missiles to Syria could threaten American and allied forces, and made clear that the United States could accept a resolution to the civil war that allows President Bashar Assad to remain in power for an unspecified time.

"We're prepared to negotiate. Is Assad prepared to negotiate, really negotiate? Is Russia prepared to bring him to the table and actually find the solution to this violence?" Kerry told reporters after meeting with British Foreign Secretary Philip Hammond.

U.S. officials said Russia sent a small number of fighter jets to a base in Syria on Friday, hours after U.S. Defense Secretary Ash Carter talked with Russia Defense Minister Sergei Shoigu in the first military contacts between the two countries in some time.

Russia says its recent military buildup in Syria is designed to fight the Islamic State group. While ISIS lacks an air force, the Russian aircraft are capable of striking ground targets and providing close air support for ground forces, said a U.S. intelligence official who spoke on condition of anonymity.

While Kerry stressed the U.S. demand that Assad must go, he stated explicitly that an acceptable resolution to the Syrian war would allow Assad to remain in place for a time before departing.

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"We're not being doctrinaire about the specific date or time -- we're open," Kerry said. "But right now, Assad has refused to have a serious discussion and Russia has refused to bring him to the table in order to do that."

-- AP