A group of Wagner mercenaries in Belarus has moved closer to the Polish border and may stage a “hybrid attack” inside the EU country by posing as illegal migrants, Poland’s Prime Minister Mateusz Morawiecki warned.

Speaking at a press conference in southern Poland on Saturday, Morawiecki said that more than 100 mercenaries had moved close to the city of Grodno, near the Suwałki Gap — a narrow strategic stretch of Polish and Lithuanian territory that separates Belarus from the Russian enclave of Kaliningrad.

“They will probably be disguised as Belarusian border guards and will help illegal immigrants to enter Polish territory, destabilize Poland,” Morawiecki said, according to Polish public broadcaster TVP.

The Wagner members would also likely “try to infiltrate Poland pretending to be illegal immigrants,” he added, saying the situation had become “more dangerous.”

In 2021, Warsaw and Brussels accused the Belarusian government and its Russian backers of seeking to sow instability at the edge of the EU by transporting migrants to the Polish border.

Morawiecki said the latest developments were “almost certainly a step towards a further hybrid attack on Polish territory.”

An unknown number of Wagner troops moved to Belarus from Russia under a deal to end the group’s 24-hour rebellion against Moscow.

Ukraine’s border guard service said earlier this month that it was assessing how many of the mercenaries had crossed into Belarus. Before the short-lived coup, Wagner troops had formed the main force fighting for the devastated Ukrainian city of Bakhmut.

On Saturday, Ukrainian President Volodymyr Zelenskyy’s official social media channels reported that he had visited front-line troops in the Bakhmut area and met with military commanders.

Zelenskyy said he could not share details on current operations. But an intelligence update by the U.K.’s Ministry of Defense on Saturday confirmed an “uptick of fighting” in two sectors in the south of Ukraine in the past two days, with the capture of the village of Staromaiorske in the Donetsk region.

Fighting was also focused on the village of Robotyne, south of Orikhiv, in the Zaporizhzhia region, the U.K. ministry said.