Poland has accused Belarus of trucking hundreds of migrants back to the border and pushing them to attempt to cross illegally, only hours after clearing camps at the frontier.
The accusation by Poland suggests that an apparent change of tack this week by Minsk has not resolved the border crisis, which has spiralled into a major East-West confrontation.
European governments accuse Belarus of flying in thousands of people from the Middle East and pushing them to attempt to cross the border illegally.
Around ten migrants are believed to have died in the freezing woods. Belarus denies fomenting the crisis deliberately.
Belarus authorities cleared the main camps yesterday where thousands of people had been huddling by the Polish border. Hundreds of Iraqis were also sent home on the first repatriation flight from Minsk in months.
But Polish Border Guard spokesperson Anna Michalska said that yesterday evening that Belarus authorities were already trucking hundreds of migrants back and forcing them to try to cross in darkness.
"(The Belarusians) were bringing more migrants to the place where there was a forced attempt to cross," Ms Michalska said.
"At the beginning there were 100 people, but then the Belarusian side brought more people in trucks. Then there were 500 people."
Fewer people are crossing the border, but some large groups can be very aggressive, she told a news conference.
When the migrants tried to cross the border, Belarusian troops blinded Polish guards with lasers, she said, adding that some migrants had thrown logs and four guards sustained minor injuries.
The migrants from the camp were taken yesterday to a large warehouse where journalists were permitted to film them.
In a hospital in Bielsk Podlaski, Poland, three migrants caught by Polish security after crossing the border were receiving treatment, including one, admitted without a passport and believed to be an Iraqi Kurd, who was in serious condition.
Mansour Nassar, 42, a father of six from Aleppo who had been living in Lebanon, said he had left some 12 days ago for Belarus and had been in the forest for five days.
"The Belarusian army told us: 'If you come back, we will kill you'" he said from his hospital bed, in tears. "We drank from ponds … Our people are always oppressed."
Human rights groups say Poland has exacerbated the humanitarian crisis with a hard line at the frontier, sending back anyone who tries to cross. Poland says this is necessary to stop more people from coming.
"I have personally listened to the appalling accounts of extreme suffering from desperate people - among whom many families, children and elderly - who spent weeks or even months in squalid and extreme conditions in the cold and wet woods due to these pushbacks," Council of Europe Commissioner for Human Rights Dunja Mijatović said today in a statement following a four-day mission to Poland.
"On some occasions, families were separated. I have witnessed clear signs of their painful ordeal: wounds, frostbite, exposure to extreme cold, exhaustion and stress," she said.
"Several people lost their lives. I have no doubt that returning any of these people to the border will lead to more extreme human suffering and more deaths."
Belarusian President Alexander Lukashenko discussed the crisis today by telephone with his ally, Russian President Vladimir Putin.
They stressed the importance of cooperation between Belarus and the EU, said the Kremlin, which has long said Europe must resolve the crisis directly with Minsk.
Europeans have shunned Mr Lukashenko since a disputed election last year, but reached out cautiously this week, with German Chancellor Angela Merkel speaking to Mr Lukashenko twice by phone.
But yesterday the European Commission and Germany rejected a proposal that Minsk said it had made to Ms Merkel, under which EU countries would take in 2,000 migrants, and 5,000 others who agreed to return home would be sent back.
The United States accused Minsk of using the migrants as "pawns in its efforts to be disruptive".
NATO Secretary-General Jens Stoltenberg said that the situation on the borders remained deeply concerning.
"Lukashenko's regime's use of vulnerable people as a means to put pressure on other countries is cynical and inhumane. NATO stands in full solidarity with all affected allies," Mr Stoltenberg told reporters on a visit to Berlin.