South Korea's military said on Thursday that its planes flew through the air defense zone this week without informing Beijing and had faced no apparent backlash. Japan also said its commercial and military planes had continued to fly in the zone.

The defiance follows a weekend declaration by China, which on Saturday published coordinates for an "East China Sea Air Defense Identification Zone (ADIZ)," including the disputed islands. The disputed islands, known as the Senkakus in Japan, and the Diayou in China, are at the center of a long-running dispute for sovereignty between Beijing and Tokyo.

The ADIZ declaration, if observed to by other nations, would give China control over airspace above some of the world's busiest international shipping lanes.

The Philippines, which also faces an increasingly bitter dispute with Beijing over islands in the South China Sea, said it had also rejected China's declaration.

The US was the first to defy the zone on Tuesday when it flew two unarmed B-52 bombers around the disputed Islands. The next day, following a request from the Japanese government, which does not recognize the ADIZ, Japan Airlines (JAL) and ANA Holdings said they had stopped giving flight plans to Chinese authorities.

Chinese air patrols

In a seeming first response to the overflights, China sent fighter jets and an early warning aircraft into the newly declared zone on Thursday, according to state media.

The Chinese planes had carried out normal air patrols on Thursday as "a defensive measure and in line with international common practices," air force spokesman Shen Jinke said in comments quoted by the Xinhua news agency.

Shen said China's air force would remain on high alert and take measures to protect the country's airspace, Xinhua reported.

China's declaration of the new zone has raised tensions in the region ahead of a trip by US Vice President Joe Biden, who is scheduled to visit Japan, China and South Korea next week.

While Washington has not taken a position on sovereignty over the islands, it recognizes Tokyo's claim to administrative control over them and it is therefore bound by treaty to defend Japan in the event of an armed conflict.

hc,tj/pfd (Reuters, AFP, AP)