China Fighter jets tail U.S and Japan fighter jet.

China launched two fighter planes Friday to investigate flights by a dozen U.S. and Japanese reconnaissance and military planes in its new maritime air defense zone over the East China Sea, state media said.

China responded on Thursday to growing international defiance of its new air-defense zone in the East China Sea both by sending advanced fighter jets to the area and trying to play down any threat of military retaliation—underlining the confusion and escalated tension over territorial disputes in East Asia.

The announcement by China's air force that it had sent fighters and an early warning aircraft to patrol the zone came just a few hours after Japan and South Korea, following the U.S. lead, said their military aircraft had flown into the zone without notifying Beijing over the past few days, and would continue to do so.

The United States and other countries have warned that the new zone could boost chances for miscalculations, accidents and conflicts, though analysts believe Beijing's move is not intended to spark any aerial confrontations but rather a long-term strategy to solidify claims to disputed territory by simply marking the area as its own.

The State Department said Wednesday it is advising U.S. airlines to take necessary steps to operate safely in China's newly declared air defense zone in the East China Sea, a day after two American B-52 bombers flew through the contested airspace.

State Department spokeswoman Jen Psaki told reporters at a daily press briefing that the U.S. is attempting to determine whether China's new air defense zone rule requiring foreign aircraft to identify themselves applies to commercial airlines, Reuters reported.