WARSAW, Poland — Polish and Lithuanian leaders held an urgent meeting Thursday in a strategically sensitive area where their NATO nations border Belarus and the Russian territory of Kaliningrad, warning that they are bracing for provocations from Moscow and Minsk in the area.

The meeting came two days after two Belarusian helicopters flew briefly at low altitude into Polish air space, in what was viewed as a provocative move. Both nations on NATO’s eastern flank have increased their border security following the arrival of thousands of Russia-linked Wagner group mercenaries just across their borders in Belarus after an aborted mutiny in Russia in June.

“Russia and Belarus are increasing the pressure on the borders, increasing the number of their provocations, and we must be aware that the number of these provocations will grow,” Polish Prime Minister Mateusz Morawiecki said at a news conference with Lithuanian President Gitanas Nauseda.

The Belarusian Foreign Ministry denied that its country’s helicopters entered Poland. Local Polish residents posted photos on social media of helicopters with Belarusian insignia flying above.

They met in Suwalki, a town in the Suwalki Gap, a sparsely populated stretch of land running 60 miles along the Polish-Lithuanian border. Also known as the Suwalki Corridor, the stretch of territory links the three Baltic states of Lithuania, Latvia and Estonia with the rest of the NATO alliance. It separates Belarus, an ally of Russia, from Kaliningrad, a heavily militarized exclave of Russia located on the Baltic Sea which is separated from the Russian mainland.

Potential Flashpoint Between NATO and Russia

Military analysts in the West have long viewed the Suwalki Gap as a potential flashpoint area in case of a standoff between Russia and NATO. They worry that if Russia were to ever seize the Suwalki Gap, it would leave Lithuania and the other two Baltic states, Latvia and Estonia, cut off from Poland and other NATO allies.

Nauseda said he believes the Suwalki Gap remains a vulnerable place, even though Sweden — located across the Baltic Sea — is on track to join NATO.

“Some people say the agreement reached at the NATO summit on Sweden’s future membership is changing the geopolitical situation, and the strategic importance of the Suwalki Corridor is diminishing. I certainly do not agree with this view and I believe that the Suwalki Corridor remains a potential target of provocation by both Russia and Belarus,” Nauseda said.

The NATO countries on the eastern flank have felt under pressure for a couple of years.

Large numbers of migrants from the Middle East and Africa began arriving two years ago at the borders of Poland, Lithuania and Latvia. European leaders have accused Belarus leader Alexander Lukashenko, an ally of Russia, of opening the migration route in an act of “hybrid warfare” aimed at creating instability in the West.

“Our borders have stopped various hybrid attacks for years. Russia and Belarus are increasing their numerous provocations and intrigues in order to destabilize the border of NATO’s eastern flank,” Morawiecki said.

“Today, the Polish borders and the border of Lithuania are the borders of the free world, which are stopping the pressure from the despotism from the east,” Morawiecki said.