Russia took the rare step of dispatching two nuclear-capable strategic bombers to patrol Belarusian airspace on Wednesday in a show of support to close ally Belarus at a time when it is locked in a migrant standoff with the European Union.
Moscow's decision to up the ante came as the 27-nation bloc considered sanctions on Wednesday to punish Minsk for what it calls an artificially created crisis, something Belarus denies.
Migrants trapped in Belarus made multiple attempts to force their way into Poland overnight, Warsaw said on Wednesday, announcing that it had reinforced the border with extra guards.
United Nations human rights chief Michelle Bachelet called on states to deescalate and resolve the "intolerable" crisis.
"These hundreds of men, women and children must not be forced to spend another night in freezing weather without adequate shelter, food, water and medical care," she said.
The EU, which has repeatedly sanctioned Belarus for human rights abuses, accuses Minsk of drawing in migrants from the Middle East, Afghanistan and Africa and then pushing them to cross into Poland to try to sow violent chaos on the bloc's eastern flank.
The bloc's 27 ambassadors agreed on Wednesday that this amounts to "hybrid warfare" by Belarusian President Alexander Lukashenko - a legal basis for new sanctions.
"We are facing a brutal hybrid attack on our EU borders. Belarus is weaponizing migrants' distress in a cynical and shocking way," EU Council President Charles Michel said.
Belarus and its ally Russia have placed the blame on Europe, with the Kremlin accusing it of failing to live up to its own humanitarian ideals and trying to "strangle" Belarus with plans to close part of the frontier. It said it was unacceptable for the EU to impose sanctions on Belarus over the crisis.
The Tupolev Tu-22M3 bombers that Russia sent to overfly Belarus are capable of carrying nuclear missiles, including hypersonic ones of the kind designed to evade sophisticated Western air defenses.
Russian Foreign Minister Sergei Lavrov said he hoped responsible Europeans would "not allow themselves to be drawn into a spiral that is fairly dangerous."
German Chancellor Angela Merkel urged Putin to put pressure on Belarus over the situation at the border, a German government spokesperson said. The Kremlin said Putin told her the EU should talk directly to Belarus.
The crisis strikes the EU in a vulnerable area.
In 2015 the bloc was deeply shaken by an influx of more than 1 million people fleeing conflict in Syria, Iraq and Afghanistan that led to deep rifts between member states, strained social security systems and fanned support for far-right parties.
The EU appears more united this time but there are some signs of internal friction with Brussels warning Poland that it should not use EU funds to erect border walls and razor wire.
Thousands of people have converged on the border this week, where makeshift razor wire fences and Polish soldiers have repeatedly blocked their entry. Some of the migrants have used logs, spades and other implements to try to break through.
"It was not a calm night. Indeed, there were many attempts to breach the Polish border," Polish Defence Minister Mariusz Blaszczak told broadcaster PR1.
Video from the border obtained by Reuters showed young children and babies among the people stuck there.
"There are lots of families here with babies between two or four months old. They have not eaten anything for the past three days," the person who provided the video told Reuters, saying they were a migrant themselves and declining to be named.
Reuters found ripped-up tickets from Middle Eastern airlines, documents from tourist agencies and receipts in the forest near the Polish town of Hajnowka at what appeared to be an abandoned campsite. Shoes, plastic water bottles, sleeping bags and garbage bags of provisions were also found.
Poland's prime minister said the EU needed to block flights from the Middle East to Belarus.
The Polish border guards service reported 599 illegal border crossing attempts on Tuesday, with 9 people detained and 48 sent back. Blaszczak said the force of Polish soldiers stationed at the border had been strengthened to 15,000 from 12,000.
The EU accuses Lukashenko of using "gangster-style" tactics in the months-long border standoff, in which at least seven migrants have died. The new EU sanctions would target around 30 individuals and entities including the Belarusian foreign minister, three EU diplomats told Reuters.
The crisis erupted after the EU, United States and Britain imposed sanctions on Belarus over its violent crackdown on mass street protests that were sparked by Lukashenko's disputed election victory in 2020.
Lukashenko turned to traditional ally Russia for support and financing to ride out the protests. Russia regards Belarus as a strategic buffer against NATO.
Poland denies accusations by humanitarian groups that it is violating the international right to asylum by hustling migrants back into Belarus instead of accepting their applications for protection. Warsaw says its actions are legal.
Some migrants have complained of being repeatedly pushed back and forth by Polish and Belarusian border guards, putting them at risk of exposure, lack of food and water.