Polish Prime Minister Mateusz Morawiecki accused Belarus of state terrorism on Wednesday as further crowds of migrants tried to breach Poland's shared border with the country.

For weeks now, people from the Middle East have been brought to Minsk by plane and taken onwards to Belarus' western borders with Poland and Lithuania, according to the Polish leader.

He described the situation at the Polish-Belarusian border as a political crisis - not a migrant crisis - with the goal of destabilizing the European Union.

"It is also a silent revenge of [Belarusian President Alexander] Lukashenko for supporting the democratic elections in Belarus last August [2020] and for supporting the democratic changes that we hoped would take place," Morawiecki said during a press conference in Warsaw with EU Council President Charles Michel.

The migrants are caught at the centre of a fierce diplomatic row between Lukashenko and the EU, which does not recognize the authoritarian ruler as a legitimate leader.

The EU accuses Minsk of orchestrating the crisis in retaliation for Western sanctions imposed on Belarus for political repression.

The bloc moved a step closer on Wednesday to penalizing Belarus for the crisis, with member states agreeing to extend an existing sanctions regime.

Poland is refusing to let the migrants onto its territory and has sent hundreds of reinforcements to the border in recent weeks. It has also erected a barbed wire fence, in an effort to stop any attempts by migrants to break through.

Earlier Wednesday, two large groups of migrants that had been stopped from moving further westwards reportedly broke through into Poland.

Polish officials then said that members of the Belarusian security forces fired their weapons, apparently in an attempt to scare the crowds. The Polish Defence Ministry released a six-second video clip on Twitter in which a shot can be heard, followed by screams.

The ministry also said that Belarusian officials were employing violence against the migrants.

Lukashenko demanded on Tuesday that they be allowed through into Poland. He said in an interview they mainly wanted to settle in Germany, not Poland.

German Chancellor Angela Merkel on Wednesday appealed to Russia to use its influence on Minsk to find a way to resolve the growing tensions in the region.

In a phone call with Vladimir Putin, Merkel told the Russian president that it was inhumane for Lukashenko to use migrants for his own ends, according to the chancellor's spokesperson.

Echoing Morawiecki's comments, spokesman Steffen Seibert accused the Belarusian government of "state smuggling and trafficking."

The problem must be solved "in a humane way," the outgoing chancellor herself said later. This was not the case at the moment, she said, adding that the migrants were "victims of misanthropic policies."

Despite increasingly tight security at the EU's external borders, hundreds of migrants have been arriving in Germany via Belarus and Poland.

Since the beginning of November, the German federal police registered a total of 1,246 unauthorized entries with reference to Belarus. Since the beginning of the year, there have been 9,087.

Fearing a repeat of the situation on their own borders, other countries are setting up barricades towards Belarus. Lithuania, where a state of emergency has been in effect at the border since midnight, has already taken such steps. On Wednesday, Ukraine boosted its border protection forces at the border with Belarus.

Svetlana Tikhanovskaya, Belarus's exiled opposition leader, whose supporters say was the true victor in last year's disputed presidential election, on Wednesday warned national governments against trying to negotiate with Lukashenko.

During a visit to Berlin, she told the Funke media group "that dialogue with the regime of Lukashenko is not possible."