MELITOPOL, Sept. 29 - Russia has left troops behind after staging war games in Belarus despite promising not to, Ukraine's Commander in Chief Viktor Muzhenko told Reuters.

In an interview on a military plane on Thursday evening, Muzhenko said Russia has withdrawn only a few units from Belarus and had lied about how many of its soldiers were there in the first place.

His comments could increase tension between the two neighbors and contradict the Belarussian defense ministry spokesman, who said the last train of Russian troops and equipment had left Belarus on Thursday.

Russian on Saturday denied the allegations.

“As for units of Russian forces that took part in a mutual strategic military exercises ‘Zapad 2017’, they all returned to their permanent disposition,” TASS news agency quoted Major-General Igor Konashenkov as saying. “Zapad” is the Russian word for “west”.

Relations between Kiev and Moscow nosedived after Russia's annexation of the Crimean peninsula in 2014 and the outbreak of a separatist insurgency in eastern Ukraine that has killed more than 10,000 people.

Ukraine sees itself as being at war with Russia and has accused Moscow of sending troops and hardware to fight in the Donbas region, which Moscow denies. There are frequent casualties despite a notional ceasefire agreed in 2015.

The Zapad wargames, held by Russian and Belarussian troops on territory in both countries in September, are a new source of concern for neighboring Ukraine and NATO member states on Europe's eastern flank.

Russia has said the exercise was to rehearse a purely defensive scenario, that the scale of the wargames was in line with international rules, and that allegations it was a springboard to invade Poland, Lithuania or Ukraine were false.

But Muzhenko said the wargames were of an offensive nature. Ukraine staged its own drills in northern Ukraine in response to Zapad and built up troops there.

"I wouldn't say that the tension has lessened. We can say tension is building up or rising," he said.

"We had information that they had withdrawn only a few units of the declared 12,500 troops, of which 3,000 were Russians, but there were significantly more of them there."

Muzhenko said the Russians had withdrawn air units from Belarus to make a show of leaving.

"Russia demonstrated, and it was primarily a demonstration, the return of aviation units -- they took off from the airfields and flew to airfields in Russia. But we understand that 300-400 km for aviation is a distance that can be overcome in a very short time," he said. (rt/ez)