Four European Union member states on Monday called on the United Nations to take action against Belarus for allowing migrants to cross illegally into the bloc.
Some EU officials recently claimed Belarus was "deliberately" sending migrants into the EU through Lithuania after thousands — mostly from the Middle East — crossed the border in recent months.
On Monday, the prime ministers of Latvia, Lithuania, Poland and Estonia said it was clear that "the ongoing crisis has been planned and systemically organized" by Belarusian President Alexander Lukashenko.
The latest row between the EU and Belarus came after the 27-member bloc imposed sanctions on Lukashenko's regime over a crackdown on Belarusian dissent following disputed presidential elections last year.
'A hybrid attack'
The four eastern European nations said in a joint statement that "using immigrants to destabilize neighboring countries constitutes a clear breach of the international law and qualifies as a hybrid attack" on them and the entire bloc.
"It is high time to bring the issue of abusing migrants on the Belarussian territory to the attention of the UN, including the United Nations Security Council," the four premiers wrote.
"We urge the UN High Commissioner for Refugees to take active steps to facilitate the solution of this situation and to require Belarus to comply with its international obligations," the statement said.
They added that "weaponizing refugees" was a grave breach of human rights and a threat to the EU's regional security.
Latvia, Lithuania, Poland and Estonia will take in the migrants crossing the border, according to the statement, but will also call for "possible new restrictive measures by the EU to prevent any further illegal immigration."
Latvia, Lithuania and Poland — which share a land border with Belarus — are all trying to block or push back migrants who attempt illegal crossings.
In May, Latvia and Lithuania raised the alarm about Belarus giving free passage to migrants. Several stand-offs have taken place at the border since then.
Lithuania is installing a metal fence armed with razor wire along its 670-kilometer (416-mile) border with Belarus.
Polish Defense Minister Mariusz Blaszczak has also said that a 2.5-meter (8.2-foot) high "solid fence" would be built along the Polish-Belarusian border.
Meanwhile, Latvia declared a state of emergency along its 175-kilometer border with Belarus to allow soldiers and police to support border guards.