Poland's Prime Minister Mateusz Morawiecki called the migrant crisis on the Belarusian-Polish border, the "greatest attempt to destabilise Europe" since the Cold War.
The premier made the remarks as he met with representatives of the three Baltic republics, at a time when Warsaw is facing not only a border crisis but heightened tensions with Brussels over allegations it is breaching its commitment to the bloc's democratic principles.
The West accuses Belarus of creating the crisis by bringing in would-be migrants – mostly from the Middle East – and taking them to the border with promises of an easy crossing into the European Union.
Belarus has denied the claim, criticising instead the EU for not taking in the migrants.
Caught in the middle, migrants often report being forced to cross the border by Belarusian officials, then pushed back into Belarus by Polish authorities.
"In the last 40 hours, Lukashenko transported migrants directly from the Polish border to logistics centres a few kilometres from the border with Latvia. This best shows that these people are an instrument in the hands of the authorities in Minsk," Morawiecki said.
"Poland will not yield to blackmail and will do everything to defend the EU's borders," he tweeted.
He went on to warn that "today the target is Poland, but tomorrow it will be Germany, Belgium, France or Spain".
Morawiecki also claimed that Lukashenko had the "backroom support" of Russian President Vladimir Putin.
Lukashenko admitted that it was "absolutely possible" his forces had helped people cross into the EU but denied orchestrating the operation.
Meanwhile, hundreds of migrants wait for their turn to cross the border or to be repatriated in a warehouse near the Bruzgi checkpoint.
The Belarusian regime wants to show that it is taking care of them and providing them with shelter and food, but Poland keeps reporting migrants' attempts to cross the border, including by some 100 "very aggressive" migrants on Sunday.
Polish media say at least 11 migrants have died since the crisis began over the summer.
According to an opinion poll released by the Rzeczpospolita daily, more than 55% of Poles are worried the border crisis could lead to an all-out war.