The accusation by Poland made clear that an apparent change of tack this week by Minsk had yet to resolve 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. Belarus denies fomenting the crisis deliberately.
Around 10 migrants are believed to have died in the freezing woods close to the border area.
Belarus authorities cleared the main camps, where thousands of people had been huddling by the Polish border, on Thursday.
On the same day, hundreds of Iraqis were sent home on the first repatriation flight from Minsk in months.
But Polish Border Guard spokeswoman Anna Michalska said that by Thursday evening 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," she said.
"At the beginning there were 100 people, but then the Belarusian side brought more people in trucks. Then there were 500 people."
The migrants from the camps were taken on Thursday to a large warehouse. Hundreds slept on mattresses on the floor.
Belarusian President Alexander Lukashenko discussed the crisis on Friday by telephone with his ally, Russian President Vladimir Putin.
They stressed the importance of co-operation between Belarus and the EU, said the Kremlin, which has long said Europe must resolve the crisis directly with Minsk.
Europeans have shunned Lukashenko and imposed sanctions on Belarus since a crackdown on protesters following a disputed election last year.
They have reached out cautiously in the past week, with German Chancellor Angela Merkel speaking to Lukashenko twice by phone.
But on Thursday the European Commission and Germany rejected a proposal Minsk said it had made to Merkel, under which EU countries would take in 2000 migrants from Belarus, and 5000 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".
Polish authorities said the cleared camp sites did appear to be empty on Friday.
"In these places it is calm ...This may mean that the current actions of Polish services at the border are effective," Polish police tweeted.
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