WARSAW, Poland -
Poland's foreign ministry said Wednesday that it summoned a Belarusian diplomat over an "intrusion" into Polish territory of "uniformed individuals armed with long guns."
Polish soldiers noticed three uniformed people with long weapons, said Stanislaw Zaryn, the spokesman for Poland's security services.
"After meeting a Polish patrol, they reloaded their weapons and then departed towards Belarus," Zaryn said.
Zaryn told The Associated Press that the incident occurred about 300 meters (300 yards) into Poland from the border with Belarus.
"It was enough to assume that it was not a mistake," he said.
The incident comes as Poland, a member of the European Union, faces significant migration pressure on its eastern border with Belarus. That border forms part of the EU's eastern frontier with autocratic Belarus.
The foreign ministry spokesman, Lukasz Jasina, said that the incident took place on the night between Monday and Tuesday.
He said that the Belarusian charge d'affaires, Alexander Chesnovsky, was summoned to Poland's Ministry of Foreign Affairs on Tuesday.
During the meeting, a deputy foreign minister, Piotr Wawrzyk, demanded an explanation and emphasized "that that the actions taken by the Belarusian authorities in recent weeks have the increasingly evident hallmarks of a deliberate escalation."
Wawrzyk "pointed out that Poland deems such actions unacceptable and won't tolerate them. He highlighted that Poland is determined to defend its borders and the external borders of the European Union," Jasina said in his statement.
There was no immediate comment from the Belarusian side.
In recent months, thousands of migrants from Syria, Iraq, Afghanistan and Africa have been lured to Belarus on tourist visas and encouraged to cross into Poland, Lithuania, and to a lesser extent Latvia -- the three EU nations bordering Belarus.
Polish and other EU leaders have accused the government of President Alexander Lukashenko, which is backed by Moscow, of encouraging the migration as a form of hybrid warfare aimed at creating instability in the region and the EU more broadly.
In Brussels, European Commission spokesman Peter Stano said Wednesday that territorial intrusion into Poland, if confirmed, "would be yet another provocation from the side of (the) Lukashenko regime against the European Union and its member states."
Zaryn said that that there has been a "series of incidents and provocations organized by Belarusians, but this was the most dangerous and serious incident so far."
He said the other incidents have involved Belarusian forces pointing guns in the air and shooting blanks when they meet Polish soldiers and guards. In other cases, Belarusian forces have destroyed a razor wire barrier on the border or encouraged migrants to do so, Zaryn said.