April 21 (UPI) -- Russian fighter planes, bombers and surveillance aircraft were intercepted over the Baltic Sea by NATO F-16s and Eurofighter planes, NATO said on Wednesday.
Two Tu-160 Blackjack bombers and an A-50 Mainstay airborne warning plane, escorted by Su-27 and Su-35 fighter aircraft, flew from Russia to the Baltic Sea and returned after about three hours on Tuesday.
Planes of NATO's Combined Air Operations Center flew from bases in Estonia, Lithuania and Poland to intercept and identify the Russian aircraft.
Some of the Russian planes flew without transponder signals, a NATO statement on Wednesday said, posing a possible hazard to civilian aircraft in the area.
The Russian planes flew in international airspace, however, as did the NATO planes.
"The event demonstrates NATO's vigilance and responsiveness to air incidents and the collective effort of our Allies to keep the airspace safe for all its users," said Brig Gen. Andrew Hansen, deputy chief of CAOC staff operations.
The incident was the latest of numerous Russian military flights to arouse the suspicion of NATO and the U.S. Northern Command.
In March, NATO fighter jets scrambled 10 times in the course of six hours to intercept six different groups of Russian military aircraft approaching NATO airspace over the North Atlantic.
Russian President Vladimir Putin, in his annual state of the nation address on Wednesday, said that any country that threatens Russia will regret it "in a way they've never regretted anything before."
The warning came after the United States last week imposed economic sanctions against Moscow for interfering in the 2020 U.S. presidential election, as well as for the SolarWinds cyberattack last year that targeted U.S. government and private computer networks.
On Monday, the U.S. State Department expressed "deep concern" over indications that Russia is targeting Ukrainian ships in the Black Sea in "another unprovoked escalation in Moscow's ongoing campaign to undermine and destabilize Ukraine."
Josep Borrell, the high representative of the European Union for foreign affairs and security policy, said on Monday that Russia has recently massed more than 150,000 troops "with all kinds of materials," including tanks, aircraft and field hospitals, at the Ukrainian borders and in annexed Crimea.