Poland accused Belarus of staging an armed cross-border intrusion and said on Wednesday it had summoned the Belarusian charge d'affaires to protest what it sees as a deliberate escalation of the migrant crisis at the frontier.

Warsaw has imposed a state of emergency at the border following a surge in migrants from countries such as Afghanistan and Iraq trying to enter Poland, a European Union member, via Belarus.

Poland's foreign ministry said unidentified uniformed individuals armed with long guns had crossed into Polish territory from Belarus on the night of Monday, Nov. 1.

"Deputy Foreign Minister Piotr Wawrzyk forwarded an emphatic protest ... against the violation of the Polish state border, emphasising that the actions taken by the Belarusian authorities in recent weeks have the increasingly evident hallmarks of a deliberate escalation," the ministry said in a statement.

"(He) pointed out that Poland deems such actions unacceptable and will not tolerate them ... and urged the Belarusian side to explain the incident immediately."

Belarusian President Alexander Lukashenko's office did not respond to a request for comment. Reuters was not immediately able to contact the Belarusian embassy in Warsaw.

Tuesday's meeting was the third time in a month that Belarusian envoy Alexander Chesnovsky had been called in to answer questions about the situation at the border, where hundreds have been trying to cross illegally every day.

The European Commission and Warsaw say the flow of migrants has been orchestrated by Belarus as a form of hybrid warfare designed to put pressure on the EU over sanctions it imposed on Minsk. Belarus has denied this.