A Russian jet flew within six metres of an RAF spy plane flying at 500mph over the Black Sea, one of two mid-air incidents last month described as “dangerous and unacceptable” by the defence secretary, John Healey.

An Su-27 jet conducted six passes in front of an unarmed RAF Rivet Joint flying close to its nose, risking a collision that could have caused a diplomatic crisis between the two countries.

On a second occasion, a Russian Su-35 jet flew sufficiently close to the British spy plane that it set off its emergency systems, including disabling the autopilot, as it conducted a surveillance mission over international airspace.

A Rivet Joint is a spy plane, with a crew of up to 30, capable of a wide range of electronic surveillance at a ranges of about 150 miles, and would have been monitoring Russian activity as part of a Nato patrol.

“This incident is another example of dangerous and unacceptable behaviour by Russian pilots, towards an unarmed aircraft operating in international airspace,” Healey said. “These actions create a serious risk of accidents and potential escalation.”

It is the most dangerous Russian action against a British Rivet Joint aircraft since a plane fired a missile over the Black Sea in 2022, the MoD said on Wednesday.

Russia has been increasing its military activity in Europe. Lithuanian politicians sheltered underground on Wednesday and air traffic at Vilnius airport was temporarily suspended after a drone violated the country’s airspace.

A day earlier, Russia’s ambassador to the UN claimed Moscow had information that Ukraine planned to launch military drones from Latvia and other Baltic states. Latvia dismissed the comments as “pure fiction”.

Two Russian frigates escorted oil tankers and a suspected arms shipment through the North Sea and Dover strait last month, their activities requiring a month-long surveillance patrol by the Royal Navy.

Last month, Healey revealed the UK had tracked three Russian submarines that loitered over critical undersea infrastructure in the North Atlantic for a month before they sailed away.

“I would like to pay tribute to the outstanding professionalism and bravery of the RAF crew who continued with their mission despite these dangerous actions,” Healey said. “Let me be very clear: This incident will not deter the UK’s commitment to defend Nato, our allies and our interests from Russian aggression.”