Polish border forces have said they were attacked with stones by migrants at the border with Belarus and responded by using water cannons against them.
Police said the migrants were given gas grenades and other weapons by Belarusian forces, who directed the entire violent operation with a drone.
The situation marked an escalation in a crisis at the eastern border of the European Union and Nato in which the lives of thousands of migrants being used as proxies by Belarus are at stake.
The Poland Border Guard posted video on Twitter showing a water cannon being directed across the border at a group of migrants in a makeshift camp in freezing weather.
Polish police said one officer was seriously injured when the migrants threw objects and he was taken by ambulance to a hospital for a likely skull fracture.
A Border Guard spokeswoman, Anna Michalska, said an estimated 2,000 migrants were at the border crossing but only about 100 were believed to be involved in attacking the Polish forces.
Police spokesman Mariusz Ciarka later said the migrants at the border crossing in Kuznica had been “pacified.” He added that the attackers were equipped with gas and gas grenades by the Belarusian services, threw stones at Polish police, and the operation was controlled by the Belarusian services using a drone.
Belarus’s State Border Guard Committee said it was investigating Poland’s use of force.
“These are considered violent actions against individuals who are on the territory of another country,” committee spokesman Anton Bychkovsky said.
The EU accuses the authoritarian regime of Belarusian President Alexander Lukashenko of orchestrating a migration crisis at the borders of three of its members - Poland, Lithuania and Latvia - to try to destabilise the 27-nation bloc.
Some of the migrants are at the border with children. Most are fleeing conflict and poverty in Syria and Iraq and hope to reach western Europe. To date there have been reports of 11 deaths.
Poland’s Defence Ministry said Belarusian forces tried to destroy fencing along the border and the Interior Ministry posted video apparently showing migrants trying to tear down a fence.
It said the migrants are using stun grenades or similar weapons given to them by Belarusian officers who are no longer trying to conceal their engagement in stirring violent incidents.
Poland has taken a tough stance, reinforcing the border with riot police and troops, rolling out coils of razor wire and making plans to build a tall steel fence. The approach has largely met with approval from other EU nations who are keen to stop the arrival of another migration wave.
But Polish authorities have also been criticised by human rights groups and others for pushing migrants back across the border and not allowing them to apply for asylum.
Russian foreign minister Sergey Lavrov called the actions of Polish forces “absolutely unacceptable”, as they “violate all conceivable norms of international humanitarian law and other agreements of the international community”.
Polish officials say Russia bears some responsibility for the crisis at the border given Moscow’s alliance with Belarus. The Russian government has denied responsibility.
The EU has been putting pressure on airlines to stop transporting Syrians, Iraqis and others to Belarus.