Lithuania said a Belarusian military helicopter crossed the EU and NATO state's border minutes before thousands of people linked hands in a human chain stretching from the capital Vilnius to the border with Belarus on Sunday.

"The Belarusian ambassador was summoned to the foreign ministry and a protest note was handed over the state border violation," the ministry said in a statement.

The Belarusian defence ministry said it had countered an "attempted violation" of its airspace by "a probe made up of eight balloons with anti-government symbols".

"Thanks to decisive action taken by the crews of Mi-24 helicopters from the air defence forces, the balloons' flight was stopped without recourse to weapons," the ministry statement said.

Belarus has been shaken by mass protests against President Alexander Lukashenko's 26-year rule.

The strongman leader has accused Western countries -- particularly Belarus's EU and NATO member neighbours -- of interference and has ordered the military to step up border security.

The Belarusian opposition has said this is an attempt by Lukashenko to divert attention away from a violent crackdown on protests.