The Pentagon Friday expressed concern by what it called "increased tensions" along the border that separates Russian-occupied Crimea from the rest of Ukraine, and accused Russian President Vladimir Putin of stoking the violence with false accusations.

"We are extremely concerned about the increased tensions near the administrative boundary between Crimea and the rest of Ukraine," said Pentagon spokesman Gordon Trowbridge. "We have urged both sides to avoid provocative steps or rhetoric that could further escalate the situation."

Russia and Ukraine stepped up their security postures after Moscow blamed Ukrainian "saboteurs" for the death of two Russian servicemembers in Crimea.

Ukraine has denied the charges, and the U.S. says there is no evidence to support Russia's accusations.

"Russia has a record of frequently levying false accusations at Ukraine to deflect attention from its own illegal actions," Trowbridge said.

The Pentagon, which has some 350 military trainers in western Ukraine, urged Russia to use its influence with separatists to end violence.

The Pentagon has observed some movement of Russian troops, and missile deployments to annexed Crimea, but says for now it's more worried about the inflammatory rhetoric coming out of Moscow than the maneuvers on the ground.

Trowbridge said Russia is continuing a pattern of provocative rhetoric using accusations with little or no actual evidence to distract attention from the illegal occupation of Ukraine territory.

The U.S. and much of the international community do not recognize Russia's annexation of Crimea from Ukraine in 2014.