Poland has arrested two Russians for allegedly distributing propaganda leaflets for mercenary group Wagner in the country's two biggest cities, Warsaw and Krakow, the interior minister said on Monday.

"Both were charged with... espionage and arrested," minister Mariusz Kaminski said on Twitter, which has been rebranded as X.

The Polish counter-intelligence agency named the two men as Alexei T. and Andrei G., without providing further personal details.

It said both Russians were detained on Friday after they distributed "around 300 leaflets in public places in Krakow and Warsaw".

The leaflets contained links to "recruitment websites" for the Wagner mercenary group, which has played a key role in Russia's war on Ukraine.

"The Russians had on them more than 3,000 propaganda leaflets promoting the Wagner group. The material was given to them in Moscow," the agency said.

The suspects, who had planned to leave Poland on Saturday, were set to receive "up to 500,000 rubles" ($5,000) for their activities, it added.

Local media reported last week that stickers promoting the mercenary group had appeared in Poland.

The stickers bore the Wagner logo, a slogan in English saying "We are here. Join us", and a QR code redirecting people to a Russian website about the mercenary group.

Poland has voiced concern about possible provocative action by fighters from the mercenary group currently based in neighbouring Belarus, an ally of the Kremlin.

Warsaw has said it will increase troop numbers at the Belarus border to 10,000.