United States Vice President Joe Biden has conveyed to Chinese President Xi Jinping “deep concerns” about China’s decision to set up an Air Defence Identification Zone (ADIZ) over the disputed East China Sea, as he held more than five hours of discussions with the Chinese leader.

China, however, defended its move as being “in line with international laws”, and asked the U.S. to “respect” the establishment of the zone, making it clear it would go ahead with plans to bolster its control over the contested area regardless of regional concerns.

Mr. Biden said he was “very direct about our firm position and our expectations in my conversations with President Xi”, in a speech to U.S. business leaders in Beijing on Thursday. He described the ADIZ move as a “recent and sudden" step that had "caused significant apprehension in the region".

Senior U.S. administration officials said Mr. Biden had indicated to the Chinese “deep concerns” on how the U.S. saw the ADIZ, and also “made clear” that the U.S. and other countries were looking at China “to take steps to lower tensions” and avoid “enforcement actions that could lead to a crisis”.

Foreign Ministry spokesperson Hong Lei told reporters on Thursday China “reiterated its principled position” during the talks. “We pointed out this action is in line with international laws and conventions,” he said. “The U.S. should respect that.”

Mr. Biden had lengthy discussions with Mr. Xi stretching over more than five and a half hours on Wednesday evening, with two hours of restricted-level talks followed by a 90-minute expanded meeting and a two-hour working dinner.

The senior administration officials, at a background briefing, expressed cautious optimism that even if China went ahead with its plan, all sides would take steps to tone down tensions.

Mr. Xi, the officials said, “listened carefully to the Vice President’s arguments about the need to create a more conducive environment too”. “Now it’s a question of behaviour and action as we go forward,” the officials said, adding that the Chinese had "taken on board" Mr. Biden's comments.

It was, however, made clear that to them that China’s move was “part of a longstanding effort” and unlikely to be withdrawn, and was not a "knee-jerk" decision.

Chinese officials have stressed that they would not consider withdrawing the move, making the point that several countries had long established such zones. They have specifically pointed out that Japan’s ADIZ was set up in 1969, and covered the disputed Senkaku or Diaoyu islands in the East China Sea that are disputed by both countries - and now fall within both air defence zones.

In brief remarks to reporters in the middle of their talks on Wednesday, Mr. Xi admitted that “regional hotspot issues keep cropping up” and that “the world as a whole is not tranquil”. Mr. Biden praised Mr. Xi for being “candid” and “constructive”, saying that "candour generates trust".

China had announced on November 23 that it would set up an ADIZ in the East China Sea, including the disputed islands and a submerged reef that is under South Korean control. The ADIZ is not a territorial claim, but a pre-defined area beyond a country’s territorial airspace within which it tracks or monitors aircraft.

China’s warning that it would take unspecified “defensive emergency” measures that may include interception of aircraft that had not notified authorities of their flight plans brought expressions of concern from the U.S., South Korea, Japan and Taiwan. China said last week it has scrambled fighter jets to tail 12 American and Japanese aircraft that had conducted patrols through the ADIZ without notifying China.

The Defence Ministry here on Tuesday released a lengthy statement in an attempt to address regional anxieties, saying the Chinese response would "generally" involve only radar identification, and that deploying fighter jets was "unnecessary" if there was no threat perception.

In Tokyo on Tuesday – the first stop of his three nation Asia tour – Mr. Biden spoke of the need for a “crisis management mechanism” to reduce tensions. He is expected to raise the idea in Seoul, the last stop of his tour, where he will arrive on Thursday and hold talks with President Park Geun-hye on Friday morning.

U.S. officials said Mr. Biden and Mr. Xi had discussed at length the situation in North Korea – an issue that actually took up more time than the ADIZ.

“I think the credibility of our argument about the impact of pressure on diplomatic solutions has been enhanced in the eyes of a number of countries, including China, by what’s happened with Iran,” the senior administration officials said referring to the recent Iran deal.

“That logic, which produced the interim deal in the Iran case, we are laying out as being what should apply in the North Korea case as well," they added, "and we’ve got a strong argument to make in that respect.”

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