Media playback is unsupported on your device Media caption Leon Panetta says closer military contact between the US and China reduces the risk of "miscalculation"

The man expected to become China's next leader, Vice-President Xi Jinping, appears in "good shape", US Defence Secretary Leon Panetta has said after talks in Beijing.

The talks marked Mr Xi's first official meeting since he went missing two weeks ago without further explanation.

His sudden absence fuelled rumours over his health and a political struggle.

Mr Xi is expected to become China's next Communist Party chief and president next month.

The country is due to hold a key party congress in coming weeks that will see major changes in the top echelons of leadership.

However, no date has been set for the conference, which will be watched closely.

Mr Panetta told the BBC his meeting with Mr Xi had been successful but he could not shed any light on the reasons for Mr Xi's temporary disappearance.

Mr Panetta is in Beijing for talks with his counterpart and top Chinese leaders, as part of an Asian tour that also includes Japan and New Zealand.

It is his first visit to China as Pentagon chief.

Back injury

Mr Panetta said after Wednesday's meeting he was "very impressed" with Mr Xi who appeared well-informed and committed to improving US-China relations.

"I found him to be very healthy, in good shape [and] very much engaged. His mind was great," Mr Panetta told the BBC.

Image caption Xi Jinping, centre, was pictured at an event in Beijing on Saturday after being absent from the public eye for two weeks

He added that the meeting lasted an hour and a half, about 30 minutes longer than planned.

"He always engages in very candid conversations, and we had a very good meeting," Mr Panetta said.

"Actually it went far beyond the time we'd thought because he was so interested in discussing the issues that were before us."

While the defence secretary was not able to explain the reasons for Mr Xi's absence, former Hong Kong leader Tung Chee-hwa told CNN on Tuesday that Mr Xi had suffered a back injury.

Mr Tung said that he believed that Mr Xi sustained the injury while swimming. Correspondents say that it was the clearest explanation so far from a top party insider.

"He hurt himself in sports and he's now recovered and he's now back at work," Mr Tung - who has strong ties with China's top leaders - said.

Sources quoted by the Reuters news agency said that Mr Xi had been obeying doctors' orders to get bed rest and undergo physiotherapy. Leaders' health is typically considered a state secret in China.

The refusal of the official media to say what had happened to Mr Xi fuelled speculation that he may have had a heart attack, a stroke, undergone emergency cancer surgery or even been the subject of an attempted assassination.

Mr Xi, accompanied by military officials, said seeing Mr Panetta reminded him of his visit to the United States in February, and that his visit would help in ''further advancing the state-to-state and military-to-military relations between our two countries".

"I sincerely wish your visit will be a good success," he said.

'Expand trust'

Mr Panetta, who met his Chinese counterpart Liang Guanglie on Tuesday, has called for closer military contact between the US and China.

Image caption Mr Xi's meeting with Mr Panetta is his first with a foreign dignitary since his two-week absence

"The key is to have senior-level interactions that we are engaging in to reduce the potential of miscalculation, and boost real understanding and expand trust between our countries," he said.

His visit comes as the US increases its military presence in Asia. Washington has stressed the shift is not directed at China, says the BBC's Martin Patience in Beijing.

But Beijing remains wary about any American moves in the region, particularly Washington's close ties with Japan.

But the US has concerns of its own, says our correspondent. It is seeking greater transparency on China's military programmes.

Mr Xi cancelled several meetings with visiting foreign dignitaries, including US Secretary of State Hillary Clinton, earlier this month.

The uncharacteristic move in a country highly conscious of protocol sparked off a series of rumours over the state of Mr Xi's health.

His ''disappearance'' and the lack of an official statement, coupled with the lack of a clear date for the party congress, also prompted speculation of a power struggle within the Communist party.

Mr Xi re-emerged in the public eye on Saturday, as state media published photographs of him attending an event.