By Ben Blanchard and Roberta Rampton
BEIJING/WASHINGTON, Nov 29 (Reuters) - China sent several fighter jets and an early warning aircraft into its new air defence zone over the East China Sea on Thursday, state news agency Xinhua said, raising the stakes in a standoff with the United States, Japan and South Korea.
Japan and South Korea also flew military aircraft through the zone on Thursday while Washington sent two unarmed B-52 bombers into the airspace earlier this week in a sign of support for its ally Japan. None of those aircraft informed Beijing.
China last week announced that foreign aircraft passing through its new air defence zone - including passenger planes - would have to identify themselves to Chinese authorities. The zone includes the skies over islands at the heart of a territorial dispute between Japan and China.
The Chinese patrol mission was "a defensive measure and in line with international common practices", Xinhua cited air force spokesman Shen Jinke as saying.
The aircraft, including Russian-designed Su-30 fighter jets, conducted routine patrols and monitored targets in the zone, Shen said.
"China's air force is on high alert and will take measures to deal with diverse air threats to firmly protect the security of the country's airspace," he said.
However, Defence Ministry spokesman Yang Yujun said it was "incorrect" to suggest China would shoot down aircraft which entered the zone without first identifying themselves. He did not elaborate.
Japan's Chief Cabinet Secretary Yoshihide Suga said on Friday he did not know if Chinese planes were in the zone but added there was no change to Tokyo's sense of alertness.
Ties between China and Japan have been strained for months by the dispute over the islands in the East China Sea, called the Diaoyu by China and the Senkaku by Japan. Washington does not take a position on the sovereignty of the islands but recognises Tokyo's administrative control and says the U.S.-Japan security pact applies to them.
China's Foreign Ministry said on Thursday that since the zone came into force there had been no impact on the safe operation of international civilian flights, although it added that China "hoped" airlines would cooperate.
Japan's two biggest airlines have defied the identification order since Wednesday at the request of the Japanese government.
BIDEN TO VISIT REGION
Although there are risks of a confrontation in the zone, U.S. and Chinese military officials have stepped up communication with each other in recent years and are in regular contact to avoid accidental clashes.
U.S. Vice President Joe Biden is visiting China, Japan and South Korea next week, and will try to diffuse tensions over the issue, senior U.S. administration officials said.
"We decline to comment on Chinese flights, but the United States will continue to partner with our allies and operate in the area as normal," a Pentagon spokesman said.
China's Defence Ministry has said that it was aware of the U.S., Japanese and South Korean military aircraft in the zone and had tracked them all.
Ties between China and Japan, often tense, have increasingly been frayed in recent years by regional rivalry, mutual mistrust over military intentions and what China feels is Japan's lack of contrition over its brutal occupation of part of China before and during World War Two.
Chinese President Xi Jinping on Thursday visited a site in eastern China connected with the country's wartime struggle against Japan, Xinhua said.
"Though life is becoming better, history can't be forgotten and those who made sacrifices for (the) new China's founding must be remembered," it quoted Xi as saying.
The Global Times, an influential tabloid published by the ruling Communist Party's official People's Daily newspaper, praised the government for its calm response in the face of "provocations", saying China would not target the United States in the zone as long as it "does not go too far".
But it warned Japan it could expect a robust response if it continued to fly military aircraft in the zone.
"If the trend continues, there will likely be frictions and confrontations and even a collision in the air ... It is therefore an urgent task for China to further train its air force to make full preparation for potential conflicts," it wrote in an editorial on Friday. (Additional reporting by Phil Stewart; Editing by Dean Yates)