Tokyo lodged a diplomatic protest with Moscow after scrambling fighter jets on Wednesday as a suspected Russian helicopter entered Japan’s northern airspace at a time of heightened tensions over Ukraine.

Japan, which has volatile ties and border disputes with key neighbours China, Russia and South Korea, routinely sends jets to defend its territorial airspace.

The country scrambled military jets 49 times in January, 142 times in December and 127 times in November, the defence ministry says. Most were to counter approaching Chinese aircraft, although many of the rest involved Russian aircraft.

On Wednesday morning, one suspected Russian helicopter flew into Japanese territorial airspace off northern Hokkaido island, Japan’s defence ministry said in a brief statement.

The Japan Air Self Defence Force scrambled an unspecified number of jets and issued warnings to the helicopter to leave.

“We lodged a protest with the Russian government today through a diplomatic channel and called for a halt to such acts,” government spokesman Hirokazu Matsuno told a routine briefing.

“Russia’s increasing activity near and in our territorial waters and airspace is worrying,” he added.

The defence ministry was analysing the intent of the flight including if it was related to the Russian assault on Ukraine, local media reported.

Japan, along with other G7 countries, has pressured Moscow over the invasion, with a series of sanctions on Russian financial institutions and chip exports.