The Lithuanian, Latvian and Estonian presidents have urged the international community to hold "the Lukashenko regime accountable for human trafficking", during a joint press conference in Vilnius on Monday.
Commenting on the current migrant crisis at the border with Belarus and Poland, the leaders of the Baltic states called for a tightening of EU asylum policy, and urged the hitherto reluctant EU executive to provide "adequate EU financial support for building physical barriers and infrastructure".
"We can see how the situation on Lithuania's border is deteriorating. This situation requires immediate solutions and actions on the European and international levels. The growing threat on the border with Belarus is not only the problem for Lithuania and Poland. We are protecting the external borders of the EU and NATO," said Lithuania's President, Gitanas Nausėda.
Nausėda added that Lithuania was ready to support Poland if it activated NATO's Article 4 to request consultations, which any member state can do if they believe their "territorial integrity, political independence or security" is in jeopardy.
In Brussels, EU foreign ministers met and agreed that their existing sanctions targeting Lukashenko and his allies will be expanded to include individuals or companies found to have encouraged border crossings.
After meeting the ministers, EU foreign policy chief Josep Borrell said the new sanctions would hit "quite an important number" of individuals and entities for "facilitating illegal border crossings into the EU".
"By expanding the scope of the sanctions we will be able to target those responsible for exploiting vulnerable migrants," Borrell added.
Diplomats said the new penalties are expected to target around 30 Belarusian officials, the state airline, and travel agencies.
Hundreds of migrants found themselves trapped at a border crossing on Monday, unable to go forward or backward between Poland and Belarus.
They had come believing the border to be open but their hopes were soon dashed.
Belarussian President Alexander Lukashenko, who has threatened retaliation over fresh sanctions, claims his people are trying to repatriate stranded migrants but many are refusing to go.
'No reason' to believe Lukashenko
"Active work is underway in this area, to convince people – please, return home. But nobody wants to go back," Lukashenko said, after claiming Belarus did not want the border situation to escalate into a "conflict".
But Lithuania's Foreign Minister Gabrielius Landsbergis warned Brussels had "no reason" to believe Lukashenko.
The Belarusian leader also suggested that, if Poland does not provide a "humanitarian corridor", Minsk could fly the migrants to Germany via its state-run airline Belavia.
"We will send them to Munich by our own planes, if necessary," Lukashenko added.
Poland's Interior Ministry said Monday that Belarusian forces were bringing groups of migrants to the Kuznica border crossing, and announced it would start building a border wall next month.
Belarus' state border committee rejected the accusation, saying the migrants had "self-organised" and that Belarusian border guards were present to "ensure safety".
Lukashenko repeated warnings that Belarus would defend itself if new sanctions are imposed.
Belarus has faced waves of EU sanctions in response to a crackdown on the opposition after last year's presidential elections and Lukashenko's decision to ground a Ryanair flight in Minsk earlier this year to detain journalist Roman Protasevich.
Lukashenko has so far weathered Belarus's growing isolation with the help of Moscow, who continues to defend the Belarusian leader.
Repatriation flights for migrants
About 2,000 people are in the migrant camp, including pregnant women and children, according to Belarus.
But Poland says there are between 3,000 and 4,000 migrants on the border. It has refused to allow the migrants in, detaining 50 on Sunday after they entered the country.
Warsaw has accused Belarus of preventing migrants from leaving.
Belavia has announced that nationals from Middle Eastern countries were banned from incoming flights from Turkey and the United Arab Emirates at their request.
The Iraqi government said Monday a first flight to repatriate its nationals who are among migrants stranded at the Belarus-Poland border will be organised on Thursday "on a voluntary basis".
Local police in Poland's Podlasie region announced that four Europeans had been detained during road checks for "aiding illegal border crossings" on November 15.
Aid agencies believe that at least 10 migrants have died so far and have warned of a humanitarian crisis unfolding as temperatures drop below freezing.