The situation at the Poland-Belarus border worsened on Monday, with Belarusian authorities saying that many hundreds of migrants had arrived at the border, and Poland reporting that some had already tried to break through.
The migrants are caught at the centre of a fierce diplomatic row between Belarusian President Alexander Lukashenko and the European Union, which does not recognize the authoritarian ruler as a legitimate leader.
One attempt to break through the border fencing occurred near the border town of Kuznica, the Defence Ministry in Warsaw wrote on Twitter.
In a video posted online, a man with a spade and another group carrying a tree trunk can be seen trying to knock through the barbed wire fence. A Polish uniformed officer sprays tear gas against the men.
Earlier, the border guards had reported that another attempt by migrants to break through the border had been thwarted.
Photos and a video by state news agency Belta published on Monday showed hundreds of people gathered near razor wire fencing, and Polish security guards lined up on the opposite side at the border. A helicopter flew overhead. Some of the migrants had lit fires or set up tents.
They were said to come from different countries. State news agency Belta quoted a migrant as saying they were Kurds, and that an estimated 1,500 people were in the area not far from the Bruzgi border crossing.
Russian state news agency TASS quoted the Belarusian border authorities as saying there were 2,000 people at the border.
The border guards of the ex-Soviet republic said they had taken "all necessary measures" to ensure security, according to Belta.
Border protection strengthened
Poland, for its part, announced earlier it would strengthen protection at the EU's external border.
"This huge group of migrants is under the control of armed Belarusian units who decide where they can and cannot go," Polish intelligence coordinator Stanislaw Zaryn wrote on Twitter.
He spoke of another hostile action against Poland by its neighbour.
Lukashenko faces international criticism for having allowed migrants to fly into Belarus from crisis regions and then transporting them to the EU border.
In response to sanctions against his country, he had declared that he would no longer stop people on their way to a better life in the West.
EU border states such as Poland are putting in measures to stop the influx, and have reported thousands of border crossings in recent months.
There have already been several deaths among migrants in the border region.
Germany is considered a major destination for the migrants. so far this year 8,833 people entered the country illegally via Belarus, federal police said.
The tempo has increased dramatically, however: in the first week of November alone the figure was 993, while there were only 26 in the whole first half of the year.
The German charities Seebruecke Deutschland and LeaveNoOne Behind are sending a bus to the border region with supplies for the migrants. They also intend to bring some of the migrants back to Germany - if they get official authorization.
Monday could mark the worst escalation at the border so far, Polish government spokesman Piotr Mueller told the PAP news agency. More border guards would be sent to the relevant sections of the border, he said.
The Ministry of Defence published aerial photos showing a large crowd of people near the border.
Tensions in Lithuania
Lithuania is also increasing its protection measures.
"We are preparing for all possible scenarios," said border guard chief Rustamas Liubajevas.
Since a disputed presidential election last year, the EU no longer recognizes Lukashenko as head of state of Belarus.
The "last dictator of Europe," as critics call him, is supported by Russian President Vladimir Putin.
The Kremlin on Monday welcomed the authorities' action in connection with the migrants.