Russian strategic nuclear bombers threatened U.S. airspace near Alaska earlier this month and F-15 jets responded by intercepting the aircraft taking part in large-scale arctic war games, according to defense officials.

The Russian war games began the same day President Obama and Russian President Vladimir Putin held a frosty summit meeting in Mexico June 18.

U.S. officials said the arctic exercises over the Russian Far East and Pacific appeared to be a further sign of Russia’s hardening posture toward the United States.

The Obama administration made no protest of the bomber intrusions, according to the officials, in line with its conciliatory "reset" policy of seeking warmer ties with Moscow.

About 30 strategic nuclear bombers and support aircraft took part in the war games that continued through June 25. The aircraft included Tu-95MS Bear H and Tu-160 Blackjack nuclear-capable bombers, along with Il-76 refueling tankers, A-50 airborne warning and control aircraft, and Su-27 and MiG-31 jet fighters. Some 200 troops also took part in the Russian Strategic Aviation forces exercise.

A spokesman for the joint U.S. Northern Command and North American Aerospace Defense command in Colorado Springs, which monitors air defense intrusions, had no immediate comment. A Pentagon spokesman declined to comment.

U.S. and Canadian F-15 and F-16 jets were involved in the intercepts that took place near the Air Identification Zone surrounding Alaskan airspace over the northern Pacific.

The exercises are part of increasingly aggressive Russian military activities in the arctic region in both the eastern and western hemispheres, which have created security worries among governments in northern Europe and Canada.

One official said the failure to publicize the threatening bomber maneuvers might have been related to Obama’s overheard promise in March to Russian President Dmitri Medvedev of "more flexibility."

According to the defense officials, the arctic bomber exercises are part of Russian efforts to assert control over vast areas of the arctic circle that are said to contain large mineral and oil deposits.

Retired Air Force Lt. Gen. Thomas McInerney, a former Alaska North American Aerospace Defense commander, said the Russian exercises should be a concern.

"The Russians continue to exercise our air defense identification zone, which shows Mr. Putin loves to let President Obama know that they still have global capability," McInerney said in an interview. "So much for reset."

McInerney also said the Obama administration kept the encounter between the bombers and U.S. fighters secret because "they obviously don’t want the world to know that the exercise was done deliberately to coincide with the Obama-Putin summit."

Obama and Putin met in Los Cabos, Mexico June 18 in what aides described later as a "businesslike" encounter. The two leaders, however, were shown in video and photos as unsmiling and displaying a cool demeanor toward each other.

Russia’s government and military have threatened preemptive military attacks on future U.S. missile defense sites in Europe as part of a Russian propaganda campaign against those defenses. Moscow views U.S. and NATO missile defenses as threatening its strategic missiles.

Defense officials said Russian bomber exercises highlight Moscow’s targeting of the U.S. missile defense base at Fort Greely, Alaska, one of two major ground-based interceptor bases that are part of a limited integrated missile defense system against North Korean and possibly future Chinese or Russian missiles.

Additionally, the bomber exercises raised concerns that Russia was simulating cruise missile strikes aimed at disrupting U.S. oil pipelines in Alaska. Currently, the state’s Trans-Alaska pipeline delivers more than 11 percent of U.S. oil.

The Russian bombers involved in the exercises are equipped with long-range precision-guided cruise missiles, including nuclear and conventional missiles.

A similar bomber exercise in 2007 involved Bear H and Blackjack bombers that conducted simulated cruise missile attacks on the United States. Those bombers operated from strategic bomber bases at Anadyr, Vorkuta, and Tiksi.

Military reference books state that Bear H bombers are deployed with six Kh-55 or Kh-55SM cruise missiles that can hit targets up to 1,800 miles away with either a high-explosive warhead or a 200-kiloton nuclear warhead.

Russian Air Force Lt. Col. Vladimir Deryabin, a Defense Ministry spokesman, told Russian state-controlled news agencies that the main purpose of the war games was to provide practice for strategic, fighter, and special aviation aircrews. The first phase involved the dispersal of aviation groups to air bases in the northern and eastern region. A second phase deployed aircraft that flew in groups with fighter cover, he said.

Deryabin said that the mission of the exercise was to "practice destruction of enemy air defenses and strategic facilities," according to a June 25 dispatch by the Russian news agency Interfax.

State Department documents made public by Wikileaks have revealed that Russian offensive military exercises in the arctic during the past several years have been aimed at Moscow’s efforts to "emerge as the dominant arctic power by default."

Such exercises have alarmed Norway’s government since many of the exercises took place near Norway’s coast.

International discussions on Russian military exercises in the arctic have been highlighted by Moscow’s failure to provide pre-flight notification of bomber exercise flights.

It could not be learned if the Russians notified the United States of the recent bomber exercises near Alaska.

Canada has complained that earlier Russian bomber flights were conducted without Russia notifying the Canadian government.

A classified 2009 cable from the U.S. Embassy Moscow said Russia in May 2009 outlined its policy toward the arctic for 2020 and beyond, and said Moscow adopted a "cold peace" policy against Europe and the United States. It stated that the region will be used for strategic resources and that Moscow is seeking to claim exclusive control over an emerging northern sea route passage.

"The Arctic region, both within Russia's legally clarified borders and in areas beyond, likely holds vast untapped resources of oil and gas," the cable states. "While many Russian analysts are skeptical that any of these resources will be economically exploitable in the near future, the Russian leadership wants to secure sovereignty over these ‘strategic’ resources."

As part of the arctic military expansion, Russia announced May 30 it was re-opening arctic air bases that had been closed after the Soviet Union collapsed in 1991.

Russian officials have said the strategic air bases will be used for arctic operations and include airfields in the far north at Naryan-Mar, on Novaya Zemlya, and Franz Josef Land.

Naryan-Mar is a mainland strategic air base and Novaya Zemlya and Franz Josef Land are islands.

Additionally, Russia has announced it is setting up an 8,000-troop Arctic Brigade that will be deployed on the Kola Peninsula, near Finland and Norway.

In 2010, Adm. James A. Winnefeld, then-commander of the Colorado-based U.S. North Command, said in an interview that Russia has continued to fly its strategic nuclear bombers near U.S. airspace as part of Moscow’s efforts to maintain what he termed the illusion of power.

"In some cases, this is about the illusion of power, where power is not quite there," Winnefeld said from the Colorado Springs-based command known as Northcom. "They are trying to show the world that they are a powerful nation, and we’re not giving them the satisfaction."