KIEV, Jan. 21 (Xinhua) -- Ukrainian authorities on Wednesday accused Russia of sending troops and armament into eastern Ukraine to support independence-seeking insurgents.

"Due to the losses incurred in military hardware and manpower, the Russian side has carried out a build-up of its occupation contingent," Andriy Lysenko, spokesman for the government's military operation in the east, told reporters during a media briefing.

Lysenko said that in recent days, "significant number" of Russian troops, at least 60 tanks, 50 armored vehicles and 100 multipurpose all-terrain infantry vehicles "Tigr" crossed into eastern Ukraine from Russia.

The spokesman, however, provided no specific evidence of Russian troops or military hardware presence in Ukraine.

Earlier in the day, Foreign Ministry spokesman Eugene Perebiynis told reporters that Kiev has asked Moscow for an explanation of what he called "concentration of about 50,000 combat-ready Russian troops along the joint border."

Russian Foreign Minister Sergey Lavrov has denied the allegations, saying nobody can present the proof of such presence.

Kiev and some Western countries have long accused Russia of direct involvement in the conflict in Ukraine, which Moscow has denied flatly.