Polish forces have fired tear gas and water cannon at people trying to cross the Belarusian border, sparking accusations from Belarus that Poland - a European Union and NATO member - is trying to escalate the crisis.
Polish border guards, who are deployed along with the army and police, estimate up to 4,000 migrants are camped out on the border between Poland and Belarus in increasingly dire conditions and freezing temperatures.
Western powers accuse Belarus leader Alexander Lukashenko of orchestrating the crisis, possibly with Russia's backing, by luring migrants to the border to sow division in the EU - claims denied by Minsk and Moscow.
A standoff near the Bruzgi-Kuznica border crossing began last week when hundreds of migrants gathered there.
"Migrants attacked our soldiers and officers with rocks and are trying to destroy the fence and cross into Poland," Poland's defence ministry said, tweeting a video showing apparent clashes at the border.
"Our forces used tear gas to quell the migrants' aggression."
Seven police officers, a border guard and a soldier were injured in the clashes, Polish officials said, with police saying stun grenades and tear gas canisters had also been thrown at officers.
The defence ministry said 15,000 troops have been deployed.
There are an estimated several hundred border guards and police officers.
The Belarusian health ministry said that around 20 migrants camping out at the border had received medical assistance in the last few days, including five people treated for eye and respiratory problems today.
Belarus also said it was setting up a "logistic centre" in the Grodno region where migrants could sleep.
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Belarusian foreign ministry spokesman Anataoly Glaz accused Poland of exacerbating the problem.
"We see today from the Polish side direct provocations and inhumane treatment of the disadvantaged," he said.
Russia also condemned Poland's use of tear gas and water cannon against the migrants, with Foreign Minister Sergei Lavrov calling it "absolutely unacceptable".
Visiting areas near the border on the Polish side, the Council of Europe human rights commissioner Dunja Mijatovic said the situation was "extremely dangerous".
"We need to find a way to de-escalate, to make sure the focus is really to stop the suffering," she told reporters.
Ms Mijatovic also called for aid groups and the media to be given "full access" as they are currently banned from the immediate area under a state of emergency law in Poland.
Mr Lukashenko, who has crushed opposition to his rule over nearly three decades in power, said that he wanted to avoid a "heated confrontation" at the border.
"The main thing now is to protect our country and our people, and not to allow clashes," he told a government meeting, according to state news agency Belta.
The Belarusian leader discussed the crisis with German Chancellor Angela Merkel yesterday, his first phone call with a western leader since he suppressed mass protests against his rule last year.
Mrs Merkel's office said the pair discussed bringing humanitarian aid to the migrants, whose number includes many young children.
Mr Lukashenko said he and the German leader agreed the standoff should be defused.
"We were of the united opinion that nobody needs escalation - not the EU, or Belarus," he said.
But Mr Lukashenko said he had "differing" views with Mrs Merkel on how the migrants got to Belarus, with the West saying Minsk had brought them there as revenge for sanctions.
EU foreign ministers agreed yesterday that existing sanctions targeting Mr Lukashenko's regime will be expanded to include individuals or companies found to have encouraged border crossings.
The United States has also vowed to expand its sanctions on Belarus.
The transatlantic military alliance NATO has also slammed Belarus and backed ally Poland.
Belarusian opposition leader Svetlana Tikhanovskaya, who lives in exile in Lithuania, welcomed the sanctions saying Mr Lukashenko had "crossed all the red lines already".
Iraq has said it will start voluntary repatriations of its citizens from Belarus this week.
The Iraqi embassy in Moscow said it would fly out around 200 people on a flight on Thursday.
But many migrants have vowed not to go back.
Meanwhile, the EU has been asking for the flights to Belarus to stop.
Turkish Airlines has banned Iraqis, Syrians and Yemenis from flying to Belarus via Turkey and private Syrian carrier Cham Wings Airlines has said it will halt flights to Minsk.
Belarus's state-run airline Belavia has also said that Syrians, Iraqis, Yemenis and Afghans are banned from incoming flights from the United Arab Emirates at Dubai's request.
At least 11 migrants have died on both sides since the influx started in the summer, according to aid groups.