Poland has said it will build a fence on its border with Belarus to curb an influx of migrants it has accused the Belarusian government of driving.
Poland and fellow EU states Lithuania and Latvia have seen sharp increases in migrants from the Middle East and Asia.
They say many of the migrants are being flown into Belarus and being pushed across border by authorities.
The EU has accused Belarus of using migrants as a weapon in response to sanctions, which it denies.
The sanctions were imposed in June over Belarusian President Alexander Lukashenko’s crackdown on protesters and the arrest of a dissident journalist on board a Ryanair flight that was forced to land in Minsk.
On Monday the prime ministers of Poland, Lithuania, Latvia and Estonia called on the United Nations to intervene in a dispute with Belarus over migration.
In a joint statement, the four countries said “the issue of abusing migrants” should be raised at the UN Security Council, an international peacekeeping body.
Poland’s Defence Minister Mariusz Blaszczak later tweeted that a 2.5m-high (8.2ft) “solid fence” would be built along his country’s border with Belarus.
“Soon I will present the details of the additional participation of the armed forces,” Mr Blaszczak wrote on Twitter.
More than 900 soldiers are already assisting guards on Poland’s 400km (248 mile) frontier with Belarus. They have laid 150km of barbed wire coils on the border.
Last week, the government said 1,935 people had tried to cross into Poland from Belarus so far this month.
Of those, 1,175 have been sent back and 760 were sent to foreigner migrant centres in Poland. In the whole of 2020, 122 people crossed the border illegally and were detained.
Poland, Latvia and Lithuania are all trying to block or push back migrants who attempt illegal crossings.
This has led to stand-offs with Belarusian border guards. In one recent incident, Belarusian officers in riot gear were filmed apparently entering Lithuanian territory to push a group of migrants over the border.
On the Poland-Belarus border, another stand-off has left a group of Afghan migrants stranded for days.
Poland’s border guard says a group of 24 migrants is sandwiched between armed guards on both sides of the border.
On Monday, Mr Lukashenko accused Poland of arranging a “border conflict” and violating Belarusian territory.
Mr Lukashenko has repeatedly warned that Belarusian authorities will no longer stop illegal migrants from crossing into the territories of EU members.
Meanwhile in Lithuania, the government said it would complete a 508km fence along its border with Belarus by September 2022.
More than 4,100 mostly Iraqi migrants have entered Lithuania illegally from Belarus so far this year.