Hundreds of migrants have camped out near the Belarusian border with Poland in freezing overnight temperatures, as Polish authorities braced for further clashes with people attempting to breach the frontier.
Thousands had converged near the Polish border on Monday, some of them using logs, spades and other implements to try to break down a border fence, escalating a months-long crisis that has prompted calls for tighter Western sanctions on Minsk.
Poland and other European Union member states accuse Belarus of encouraging illegal migrants from the Middle East, Afghanistan and Africa to cross the border into the EU in revenge for sanctions slapped on Minsk over human rights abuses.
"The Belarusian regime is attacking the Polish border, the EU, in an unparallelled manner," Polish President Andrzej Duda told a news conference in Warsaw.
"We currently have a camp of migrants who are blocked from the Belarusian side. There are about 1000 people there, mostly young men. These are aggressive actions that we must repel, fulfilling our obligations as a member of the European Union."
A spokesman for Poland's special services, Stanislaw Zaryn, said Belarusian security personnel were "firing empty shots into the air, simulating dangerous events" to further destabilise the situation at the border.
"We also know the Belarusian authorities are helping migrants to destroy the border barriers. We see how they bring them tools to cut wires... to destroy the fence," he added.
Belarusian President Alexander Lukashenko's government, which is backed by Russia, denies manufacturing the migrant crisis and blames Europe and the United States for the plight of the people stranded at the border.
Polish Prime Minister Mateusz Morawiecki visited the area early on Tuesday to show support for the thousands of additional soldiers, police and border guards deployed there.
Footage published by the Polish police on Tuesday showed migrants' tents and campfires on the Belarusian side of the barbed wire fence. Poland's Border Guard said it had registered 309 attempts to cross the border illegally on Monday and 17 people, mainly Iraqis, had been detained.
Around 800 people are currently camped out on the Belarusian side of the fence, the Border Guard told Reuters. Poland's special services said as many as 12,000 migrants may currently be in Belarus.
Polish authorities shut an official border crossing with Belarus at 6am on Tuesday near where thousands of migrants had tried to push through the day before.
In Belarus's contested presidential election in 2020 Lukashenko claimed a sixth successive term, triggering mass street protests that were violently quelled by security forces.
The US, European Union and Britain imposed sanctions on Minsk.
They have accused Lukashenko and his security forces of encouraging and sometimes shepherding the migrants to cross the EU border through Poland and Lithuania in in revenge for the sanctions.
The Kremlin on Tuesday praised what it called the "responsible" work of Belarusian security personnel at the border and said it was in close contact with Minsk over the crisis. It called on all sides to act responsibly.
Humanitarian groups accuse Poland's ruling nationalists of violating the international right to asylum by pushing the migrants back into Belarus instead of accepting their applications for protection. Poland says its actions are legal.
A poll by IBRiS for Polish daily Rzeczpospolita this week showed some 55 per cent of Poles believe migrants who have illegally crossed the border should be pushed back, while a third don't.
Poland says seven migrants to date have been found dead on its side of the border, with reports of more deaths in Belarus.
A statement by the Belarusian defence ministry said Poland had violated bilateral agreements by deploying additional troops at the border and said Warsaw was not interested in constructive solutions.