Russian President Vladimir Putin and Belarusian leader Alexander Lukashenko will meet Sunday, the Kremlin said, two days after Moscow warned that any aggression against the its neighbor and staunchest ally would be considered an attack on Russia.

After Poland decided earlier this week to move military units closer to its border with Belarus in response to the arrival in Belarus of forces from Russia's Wagner Group, Putin said Moscow would use all means it has to react to any hostility towards Minsk.

The Kremlin said Lukashenko is paying a working visit to Russia and will talk to Putin about further development of the countries' "strategic partnership."

While not sending his own troops to Ukraine, Lukashenko allowed Moscow to use Belarusian territory to launch its full-scale invasion on Ukraine in February 2022 and has since met with Putin frequently.

The two countries have since held multiple joint military training exercises, and in June Lukashenko allowed his country to be used as a base for Russian nuclear weapons, a move broadly condemned by the West.

The perception that Lukashenko, a pariah in the West, depends on Putin for his survival had fanned fears in Kyiv that Putin would pressure him to join a fresh ground offensive and open a new front in Russia's faltering invasion of Ukraine.

On Thursday, the Belarusian defense ministry said Wagner Group mercenaries have started to train Belarusian special forces at a military range just a few miles from the border with NATO-member Poland.

Wagner chief Yevgeny Prigozhin was shown in a video welcoming his fighters to Belarus on Wednesday, telling them they would take no further part for now in the war in Ukraine but ordering them to gather strength for Wagner's operations in Africa while they trained the Belarusian army.