Andrius Sytas

Smuggling balloons floating over the border from Belarus have shut down the airport in Lithuania's capital Vilnius for four evenings over the past week, with authorities branding it a "hybrid attack" by the Kremlin ally.

Lithuania's Prime Minister Inga Ruginiene said on Monday her country will begin to shoot down smuggler balloons crossing the border from Belarus, which have repeatedly interrupted the Baltic nation's air traffic.

European Union member state Lithuania will close its border with Belarus if smuggler balloons enter from the neighbouring country again, Prime Minister Inga Ruginiene said on Wednesday.

Lithuania suspended air traffic at Vilnius Airport late on Tuesday due to a presence of dozens of smugglers' balloons in its airspace, the country's National Crisis Management Centre (NCMC) said in a statement.

The three Baltic states are drawing up contingency plans to deal with the possibility of hundreds of thousands of people fleeing a troop buildup or attack.

NATO said the new measures include surveillance systems and a frigate, expanding the mission launched to protect Baltic Sea infrastructure.

Latvian President Edgars Rinkevics urged NATO on Saturday to increase its protection of the Baltic States, citing Russian violations of the alliance's airspace, and adding to a similar call from Lithuania.

Lithuania's parliament granted the Baltic country's armed forces powers on Tuesday to shoot down any unmanned drone violating its airspace following incidents in which it said two Russian drones crashed on its territory.

Russia's defense ministry said the jets flew over neutral waters.

Belarus released 52 prisoners of various nationalities on Thursday after an appeal from U.S. President Donald Trump, and they headed to Lithuania with the U.S. delegation that negotiated their release, the U.S. embassy in Vilnius said.