Poland expressed “a very firm protest” against Belarus on Wednesday as Warsaw summoned Minsk’s charge d’affaires, after two military helicopters reportedly entered Polish airspace on Tuesday, Paralel.Az reports citing CNN.

“We issued a very firm protest against Belarus’ actions which we perceive as provocations,” Polish Deputy Foreign Minister Paweł Jabłoński told Polish radio station RMF.FM, adding that there could be more provocations from the Belarusian and Russian sides in the future.

The Belarusian military has denied a violation took place.

Poland has also informed NATO of the alleged helicopter incident, its defense ministry said Tuesday.