March 2 (UPI) — Japan scrambled a fighter jet on Wednesday in response to what appeared to be a Russian helicopter entering its airspace, the country’s military said, amid heightened tensions over the crisis in Ukraine.

The helicopter crossed into Japanese airspace over waters off of the northern island of Hokkaido at 10:43 a.m., the defense ministry said in a brief statement. Japan issued warnings and sent an Air Self-Defense Force fighter to respond to the incursion, the ministry said.

Japan’s military will “continue to take all possible measures 24 hours a day, 365 days a year to protect Japan’s territory and the peaceful lives of its people,” the joint staff of the defense ministry said in a tweet.

Tokyo issued a protest with the Russian government through a diplomatic channel, Chief Cabinet Secretary Hirokazu Matsuno said at a press conference on Wednesday.

Matsuno called the incident “extremely regrettable” and said Japan would continue to monitor the situation.

The incursion came as countries around the world are on alert over Russia’s ongoing invasion of Ukraine. Japan has joined Western nations in imposing a series of punishing sanctions on Moscow, including freezing the Russian central bank’s foreign exchange assets and banning some Russian banks from the SWIFT international banking network.

Japanese companies have also been on guard after a cyberattack on a supplier for Toyota forced the automaker to suspend operations at all of its domestic plants for the entire day Tuesday. The source of the cyberattack has not yet been made clear.

Tokyo has a longstanding territorial dispute with Moscow over four islands located off of Hokkaido, which has stood in the way of the two governments signing a peace treaty since the end of World War II.