Tensions rose on Tuesday on the Belarusian side of the Bruzgi/Kuźnica border crossing, where large groups of migrants had been encamped since the start of this week, Poland's PAP news agency reported.
Groups of aggressive men began throwing stones and other objects at Polish officers, while Polish border forces responded by using water cannon in an operation that lasted two hours, officials told reporters.
Commenting on these developments, Poland's police chief Jarosław Szymczyk said in a media interview on Tuesday that prosecutors in the town of Sokółka had launched an investigation into the assault on Polish police officers, border guards and troops.
He added the scene of the clashes was being examined. "We are collecting all the objects which had been thrown towards those who stood guard on the Polish border, and repelled this brutal attack," Szymczyk said.
"This will show what we were up against," he added.
He said a total of 12 Polish officers suffered injuries, including nine policemen and women, two border guards and a soldier. Earlier reports put the number of those injured at nine.
The attacks were mounted "mainly by young and unusually aggressive men," but the masked assailants seemed "well-trained and experienced in various forms of combat," Szymczyk said in the interview.
"In my assessment, the most aggressive among them were people from Belarusian security services, who were the instigators," he added.
Gen. Jarosław Szymczyk. Photo: Wojciech Kusiński/Polish Radio
The migrant crisis has grown since the summer, with Poland, the European Union and its member states, as well as NATO and the United States accusing Alexander Lukashenko, the autocratic leader of Belarus, of orchestrating the standoff in retaliation for Western sanctions against his regime.
EU foreign ministers on Monday gave the green light for a widening of the sanctions in response to Minsk's actions.
Lukashenko has denied luring vulnerable people, including Kurds from the Middle East, with the false promise of easy access to the EU and sending them over the bloc's border.
Tensions at the Polish-Belarusian border
Earlier on Tuesday, Poland's Border Guard said it had recorded 224 illegal attempts to cross from Belarus over the past 24 hours. Since the start of the year, over 33,000 such attempts have been recorded, the PAP news agency reported.
Since September 2, Warsaw has kept the border zone under a state of emergency in the face of the migrant pressure.
Poland also plans to build a solid fence along the Belarus frontier, crowned with barbed wire and fitted with electronic surveillance devices. The protective wall is due to be ready by mid-2022.
EU, NATO, US, UN nations condemn Belarus
The United States has called on Russia to use its influence over Belarus "to cease its callous exploitation and coercion of vulnerable people," White House spokeswoman Jen Psaki said on Monday amid the deepening migrant crisis on the Polish-Belarusian border.
US State Secretary Antony Blinken at the weekend reaffirmed America's support for Poland amid the crisis on the EU member's border with Belarus.
The United States and European members of the UN Security Council last week condemned Belarus for the “orchestrated instrumentalization" of migrants as tensions rose along the Polish-Belarusian border.
The Polish prime minister has said that NATO must take steps to help resolve the crisis on the Belarus border, adding that Poland and the Baltic states of Lithuania and Latvia may ask for consultations under Article 4 of the alliance's treaty.
Polish lawmakers have begun debating legislation to strengthen the country's frontiers amid rising tensions on the border with Belarus.