According to the United Kingdom Ministry of Defence's web page, British Typhoons intercepted three military transport aircraft flying in international airspace without transponders turned on, presenting a potential hazard to civilian air traffic.
"The military transport aircraft identified as AN-26 ‘Curl, AN-12 ‘Cub’ and IL-76 ‘Candid’ were intercepted as they were not transmitting a recognised identification code and were unresponsive," the MoD said.
UK Defence Secretary Michael Fallon described the Russian flights as "an act of aggression".
"We were able to instantly respond to this act of Russian aggression - demonstration of our commitment to NATO’s collective defence," Fallon said.
Nor were the three transport planes the only Russian aircraft active over the Baltic. The Latvian Armed Forces Twitter feed said six more planes had been identified: two Su-24 attack aircraft of the kind recently involved in an incident with the USS Donald Cook and four Su-27 fighters.
12.05. patruļlidmašīnas virs Baltijas jūras neitr. ūdeņiem pie LV terit. ūdeņu ārējās robežas identificēja RU BS lidm. 2x Su-24 un 4x Su-27.— NBS (@Latvijas_armija) May 12, 2016
In addition a Russian naval vessel named as the 'Zhigulevsk' (a well-known spy ship) was identified in Latvia's exclusive economic zone, 4 nautical miles (9 km) from territorial waters.