Around 80% of NATO's missions in the past year were in response to flights by Russian military aircraft flying too close to members' airspace, the alliance has said.

NATO fighter jets were scrambled hundreds of times this year to intercept aircraft, most of them Russian warplanes, the military alliance said on Tuesday.

According to NATO, 290 of around 370 total missions were flown in 2021 in response to the activities of Russian aircraft.

Most of the intercepts in 2021 took place in the Baltic region, where NATO operates an air-policing mission for Estonia, Latvia and Lithuania. 

"Generally, intercepts occurred without incident as NATO planes take off to identify the approaching aircraft and escort it out of the area. Very few intercepted flights entered allied airspace,'' NATO said in a statement.

NATO 'vigilant' of unverified flights

NATO intercept flights are a routine occurrence. But despite escalating tensions between the alliance and Moscow, the number of Russia-linked intercepts declined this year.

US intelligence has warned of a potential Russian military offensive against Ukraine over the deployment of Russian armed forces near its neighbor's borders in recent months.

In 2020, NATO jets scrambled around 350 times in response to Russian aircraft.

Across Europe, more than 60 NATO jets are on high alert at all times, ready to respond to unannounced military flights as well as to civilian aircraft losing communication with air traffic controllers, for example in the instance of a hijacking or technical problems.

"NATO fighter jets are on duty around the clock, ready to take off in case of unverified flights near the airspace of our allies," said NATO spokesperson Oana Lungescu. "NATO is vigilant, and we will always do what it takes to protect and defend all allies."

The 30-country US-led alliance has two air operations centers — one in Germany, covering northern Europe and one in Spain covering the south.