Lithuania on Tuesday asked NATO for"immediate measures" to bolster its air defences after revealing that a Russian drone that flew into the Baltic state last week was carrying explosives.

Foreign Minister Kestutis Budrys said he and Defence Minister Dovile Sakaliene had written to NATO chief Mark Rutte to ask for"immediate measures to enhance air defence capabilities in Lithuania".

Writing on X, Budrys said"a Russian military drone violated Lithuanian airspace" on July 28.

The drone, which was spotted by eyewitnesses over parts of the country's capital Vilnius, was eventually found in a military training area on August 1.

Prosecutor-general Nida Grunskiene said it was"carrying an explosive device, which was successfully neutralised by Lithuanian armed forces specialists at the scene".

"One of the main theories of the investigation is that the unmanned aircraft accidentally entered Lithuanian territory.

"I would like to stress that other theories are being investigated in parallel,"  she said.

Officials believe it to be a Russian-made Gerbera drone – a type usually used as a decoy in Russia's strikes against Ukraine.

"This marks the second such incident in less than a month. Similar airspace violations have also been reported recently by other allies," Budrys said.

"The threat is real and growing," he said.

Budrys said neighbouring Belarus, a key ally of Moscow, had a responsibility to prevent such incidents.

"If Belarus fails to take action to minimise the potential damage on our side, Lithuania will respond with political and other measures," he said.