Two U.S. Air Force B-52 long range bombers flew what U.S. officials are calling a "routine training mission" through airspace over the East China that China is claiming as a new air defense identification zone. Entering the zone without notifying Chinese authorities on Monday was the first U.S. challenge to China's controversial move that has increased tensions in the region.

Pentagon spokesman Col. Steve Warren told reporters today that two unarmed aircraft flew the "routine training mission" from Guam and spent about an hour inside the airspace designated by China on Saturday as its air defense identification zone (ADIZ). Warren characterized the mission as having "happened without incident." A separate American defense official identified the two aircraft as B-52's based at Andersen Air Force Base in Guam.

On Saturday, China's Defense Ministry announced it was establishing the zone in the airspace above the East China Sea to protect against "potential air threats" and would require military aircraft entering the zone to file flight plans and maintain radio contact with Chinese authorities. A Defense Ministry statement said , "China's armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions. "

Stretching from South Korea to Taiwan, the zone includes the disputed Senkaku island chain that is administered by Japan, but which China has claimed are Chinese territory. An American defense official confirmed that the B-52 flight plan took the bombers near the island chain.

China has been critical of Japanese and American expressions of concern about the establishment of the zone. On Monday, White House spokesman Josh Earnest described China's action as "unnecessarily inflammatory."

In a statement released over the weekend Defense Secretary Chuck Hagel said that China's announcement "will not in any way change how the United States conducts military operations in the region."

On Monday Col. Warren reaffirmed Hagel's statement and added that "when we fly into this ADIZ we will not register a flight plan, we will not identify our transponder, our radio frequency and logo. "

Warren said Tuesday that the U.S. military did not file flight plans with China about the B-52 flight into the zone and that the aircraft's crew did not make radio contact with Chinese authorities.

Warren described the B-52 flight as a "global power training sortie" that was part of a long-planned exercise called "Coral Lightning."

A defense official explained that the timing of the B-52 training mission was coincidental to China's weekend announcement establishing the zone. However, the official acknowledged that the mission was allowed to proceed given Hagel's statement that there would be no change to U.S. flight operations in the area.

Japan operates its own ADIZ that extends 200 miles from its territory.