"The behaviour of the Polish side is absolutely unacceptable," he told a press conference in Moscow, citing "tear gas and a water cannon and shots fired above the heads of migrants towards the direction of Belarus".

Thousands of migrants have camped at the Poland-Belarus border in a crisis Brussels says was orchestrated by Minsk possibly with the backing of Moscow.

Minsk and Moscow deny the claims and Russia has stood by its ally in the stand-off.

Polish forces fired tear gas at stone-throwing migrants trying to cross the border from Belarus on Tuesday, Warsaw said.

Warsaw said a Polish police officer was seriously injured in the border clashes.

Polish border guards estimate up to 4,000 migrants are now camped out along its border with Belarus in increasingly dire conditions and freezing temperatures.

Most of the migrants are from the Middle East, with many from Iraqi Kurdistan.

Iraq's embassy in Moscow said Tuesday that it will fly out around 200 people from Belarus on Thursday

Baghdad had earlier said it would organise repatriations on a "voluntary" basis.

At least 11 migrants have died on both sides since the influx started in the summer.