US Defense Secretary Leon Panetta departs this weekend on an Asian tour with stops in China, Japan and New Zealand, officials said Thursday, but it was unclear if he would meet Beijing's leader-in-waiting, whose whereabouts have been the subject of intense speculation.

Panetta's visit to China, his first as Pentagon chief, comes amid swirling rumors over the political fate of Chinese Vice President Xi Jinping, who has virtually disappeared from public view in the past two weeks.

Xi made his first public communication through state media on Thursday but has not been seen in public for 13 days.

Asked if Panetta was due to meet Xi, Pentagon spokesman George Little said: "This is not something I would comment on. This is for the Chinese to discuss, of course."

The US delegation looked forward "to meetings with top Chinese military leaders" but "the itinerary hasn't been locked in stone," Little told a news conference.

"We believe this will be a very productive and cordial visit, one that will advance our shared goals of a more transparent and even more viable relationship with the Chinese military," he added.

Panetta's trip marks his third to Asia in 11 months, underscoring President Barack Obama's bid to "rebalance" Washington's focus towards the region.

Despite the much-publicized shift to the Asia-Pacific, the Obama administration has been forced to confront a series of crises in the Middle East, with a deadly attack on the US consulate in Libya on Tuesday blamed on Islamist militants.

Before his visit to China, Panetta will fly to Japan, where US plans to deploy tilt-rotor Osprey aircraft at an American military base on Okinawa has sparked protests.

"We've been in close consultation with Japanese defense officials about the MV-22 Osprey aircraft," Little said.

Pentagon officials have sought to reassure their Japanese counterparts on the safety of the Osprey, briefing them on the circumstances of an April crash in Morocco that killed two US Marines.

"We have briefed them on the event that caused them concern in Japan. And we believe that this deployment remains on track," he said.

The Osprey, which can take off like a helicopter and then rotate its motors down enabling it to fly like a turboprop plane, was plagued by crashes and technical problems in its early phase but US commanders insist the aircraft is safe, with Marines relying on them in Afghanistan.

Tens of thousands of people staged protests in Okinawa over the weekend, demanding the US scrap plans to move 12 of the aircraft to the southern island.

The Pentagon said that Japan had made no request to alter plans to deploy the aircraft.

"I'm unaware of any request to postpone the deployment or operation of the Osprey. I don't have a time line for when the Osprey will go fully operational, but, as I said, we believe the deployment remains on track," Little said.

After stops in Tokyo and Beijing, Panetta will head to New Zealand, the first US defense secretary to visit the country in more than 30 years, officials said.

Panetta's trip to New Zealand follows the signing of a cooperation agreement in June between the two defense ministries.