PM Mateusz Morawiecki expresses concern over movement of Russian mercenary fighters in Belarus near the Polish border.

“We have information that more than 100 Wagner mercenaries have advanced towards the Suwalki Gap, not far from Grodno in Belarus,” Morawiecki told a news conference on Saturday.

This makes the situation on the border “even more threatening”, Morawiecki warned during a visit to an arms factory in Gliwice in southern Poland.

Grodno is located in the west of Belarus, about 15km (nine miles) from its border with NATO members Poland and Lithuania. The Suwalki Gap is a narrow strategic land corridor on their territory between Belarus and Russia’s Baltic exclave of Kaliningrad.

Poland, a member of both the European Union and NATO, has worried about its security with Russian ally Belarus and Ukraine on its eastern border.

Those fears have grown since Wagner group mercenaries arrived in Belarus after the group’s short-lived rebellion earlier this year.

The Poland-Belarus border has already been a tense place for a couple of years, ever since large numbers of refugees and migrants from the Middle East and Africa began arriving, seeking to enter the EU by crossing into Poland, as well as Lithuania.

Poland’s government accuses Russia and Belarus of using the migrants to destabilise Poland and other EU countries. It calls the migration a form of hybrid warfare, and has responded by building a high wall along part of its border with Belarus.

Earlier this month, Poland began moving more than 1,000 troops to the east of the country amid rising concerns that the presence of Wagner fighters in Belarus could lead to increased tension on its border.

Morawiecki noted that 16,000 attempted border crossings by migrants from Belarus had been recorded so far this year. Belarusian President Alexander Lukashenko and Russian President Vladimir Putin wanted to “push them through to Poland,” he said.

“The situation is getting increasingly dangerous … Most likely they [the Wagner personnel] will be disguised as the Belarusian border guard and help illegal migrants get to the Polish territory [and] destabilise Poland,” he said.

On Friday, Poland’s governing party chairman, Jaroslaw Kaczynski, said that Wagner fighters “are not in Belarus for fun”.

“They are there to create various types of crises, primarily directed against Poland,” Kaczynski said, adding that Poland has been building up its defence capabilities “so that these provocations, these activities, fail”.

Kaczynski’s comments came on the same day that Lithuania’s deputy interior minister warned of the possibility of his country closing its border with Belarus.

Arnoldas Abramavicius told reporters that Wagner mercenaries could disguise themselves as asylum seekers trying to cross Belarus’s borders with EU member states, or stage provocations involving refugees.

“It could be some groups of refugees, irregular migrants being transferred in order to cause some kind of unrest,” Abramavicius said.