MOSCOW — Ukraine accused Russia on Friday of dispatching tanks, troops and other weaponry across the border to bolster separatists who control a small eastern portion of Ukraine, the latest in a series of charges and countercharges that are gradually undermining a tenuous peace plan signed two months ago.

Speaking in Kiev, the capital, Col. Andriy Lysenko, a Ukrainian military spokesman, said 32 tanks, 16 howitzers and 30 trucks hauling ammunition and fighters had crossed into the Luhansk region from Russia.

He presented no clear evidence to support the claim, nor did the wealth of social media outlets in eastern Ukraine display any footage of a tank convoy. The Kiev government frequently made such claims that could not be substantiated during intense fighting between Ukrainian government troops and separatists earlier this year.

Neither NATO nor the Organization for Security and Cooperation in Europe, which is monitoring a cease-fire, could confirm the report. NATO issued a statement in Brussels saying it had noticed increased military activity along the frontier.