Ukraine's leader has accused Russia of increasing its military presence in eastern Ukraine, hours after Russian President Vladimir Putin said he wanted to see the armed conflict there ended as quickly as possible.

During a visit to NATO headquarters, Ukrainian President Petro Poroshenko said Thursday there was a "growing military presence of Russia in the region, in particular in the Donbass."

Poroshenko also said that earlier in the day, Putin acknowledged for the first time that the Russian military is present in Ukraine.

Putin told a news conference in Moscow that although Russia has no regular troops in Ukraine, there are some people "performing military tasks."

NATO secretary-general Jens Stoltenberg, Poroshenko's host, commented that "that is what we commonly call soldiers."