(CNN) -- Two U.S. military aircraft flew into China's newly claimed and challenged air defense zone over the East China Sea, a U.S. official said, an action that could inflame tensions between the world powers.

The U.S. Air Force B-52 planes -- which were not armed because they were on a training mission -- set off Monday from Guam and returned there without incident. The mission lasted for several hours, and the aircraft were in China's newly declared air zone for about an hour, according to the U.S. official.

http://edition.cnn.com/2013/11/26/world/asia/china-us-b52s/index.html?iid=article_sidebar