Russian military aircraft were intercepted by British and Norwegian jets Friday after they breached NATO airspace close to the U.K. and Finland, defense officials said.

Finland's prime minister demanded an explanation from Moscow. Interception of Russian warplanes in NATO patrolled-airspace has become increasingly common since the Kremlin ordered strategic bombers to carry out long-range missions for the first time since the breakup of the Soviet Union.

British fighter jets intercepted two Russian long-range bombers flying in NATO airspace and shadowed them until they charged course, Britain's defense ministry said, without revealing precisely where the incursion took place. The two Tu-160 "Blackjack" bombers were initially intercepted by Norwegian F16s, defense officials said.

In Finland, authorities said an Ilyushin-76 transporter plane flew about three miles into Finnish airspace for three minutes.

"These kinds of (violations) must not happen," Finnish Prime Minister Matti Vanhanen said. "And when they do happen, then they need to be sorted out between the countries in question."

Russian Air Force spokesman Col. Alexander Drobyshevsky said Friday that "all flights of our strategic bombers have been conducted in accordance with international rules."

"Our planes have flown over neutral waters without approaching air borders of any foreign nation," Drobyshevsky said, according to the ITAR-Tass news agency.

International airspace along the southern Finnish coast is narrow, and officials expected violations, military officials in Finland said.

"There's a lot of Russian airborne activity above the Gulf of Finland, especially between Kaliningrad and the Russian mainland," military spokesman Marko Luotonen said. Russian planes, mostly military transporters, frequently fly between the Baltic port enclave of Kaliningrad and bases near the city St. Petersburg.

Last month, Russian bombers approached the Pacific Island of Guam — home to a major U.S. military base — for the first time since the Cold War. In July, Norwegian F-16s were also scrambled when Tu-95s headed south along the Norwegian coast in international air space.

"The re-emergence of long-range flights from Russia is something the Russians are entitled to do, all countries have the right to maintain or upgrade and exercise their defense capabilities," Britain's military said in a statement. "The motivation behind any Russian military activity is a matter for the Russian government."

Last year, Russia apologized for violations of Finnish airspace, following about a dozen such incidents over a period of two years.

Similar complaints of air violations have been made by Finland's southern neighbors, Estonia and the other Baltic states. In October 2005, a Russian fighter jet crashed in Lithuania.