WASHINGTON — Hundreds of Russian troops are still training and equipping separatists in Ukraine, NATO’s top military commander said Monday, activities that are heightening tensions with the West and Ukraine’s government that were aggravated by Sunday’s elections in the breakaway regions of eastern Ukraine.

As the Russian Foreign Ministry appears to be moving toward recognizing the results of the voting, which was dismissed by the United States as a “sham,” Western officials are increasingly concerned that the Kremlin may be taking the steps necessary to establish an enclave that remains outside Kiev’s control.

During a visit to the Pentagon, the commander, Gen. Philip M. Breedlove, echoed those worries, telling reporters that “I am concerned that the conditions are there that could create a frozen conflict.”

Moscow followed that blueprint after the war with Georgia in 2008, establishing enclaves in Abkhazia and South Ossetia to ensure that the territorially compromised nation could not join NATO. It did the same earlier with Transnistria, a breakaway territory of Moldova where Russians have been stationed.