Image copyright Reuters Image caption Both China and Japan have sent vessels to the waters around the disputed islands

China's leader-in-waiting, Xi Jinping, has said that Japan should "rein in its behaviour" and stop undermining Chinese sovereignty, state media have reported.

His comments follow days of sometimes violent anti-Japanese protests in China over a chain of disputed islands in the East China Sea.

Mr Xi said that Tokyo's purchase of the islands from private owners last week was a "farce", Xinhua reported.

The move triggered a wave of protests across China.

In some cities on Tuesday, Japanese shops and businesses were attacked amid heightened tension on the anniversary of an incident in 1931 which led to Japan's invasion of north-east China.

Thousands of protesters chanted slogans outside the Japanese embassy in Beijing as riot police lined the streets.

The islands - known as the Senkaku islands in Japan and the Diaoyu islands in China - are claimed by both countries and have long been a point of contention. More recently there have been fears of naval conflict between the two countries.

Media playback is unsupported on your device Media caption Leon Panetta: ''These kinds of incidents could drag the US into it in one way or another"

Territorial dispute

Mr Xi, expected to become China's next leader, made the remarks during a meeting with US Defence Secretary Leon Panetta who is currently in Beijing as part of a regional tour.

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

His disappearance fuelled widespread rumours over his health and a political struggle.

But Mr Panetta told the BBC that Mr Xi appeared "in good shape".

"I found him not only to be healthy, but very much engaged in the issues that were before us," Mr Panetta said, adding that the meeting lasted half an hour longer than planned.

Chinese officials have called on the US to remain neutral in their ongoing territorial dispute with Tokyo.

Mr Panetta sought to reassure Beijing on Wednesday that his country's strategic shift towards the Pacific was not an attempt to curb Chinese power.

"Our rebalance to the Asia-Pacific region... is an attempt to engage China and expand its role in the Pacific," he said.

"It's about creating a new model in the relationship of our two Pacific powers," he told cadets at an armoured force engineering academy.

The defence secretary said that as the world's two biggest economies, the two countries must forge stronger ties between their armies to avoid potential crises.

"Our goal is to make sure that no dispute or misunderstanding escalates into unwanted tensions or a conflict," Mr Panetta said.

Correspondents say that his remarks are the latest effort by Washington to bolster military relations with the People's Liberation Army, which has in the past been reluctant to promote contacts with the US top brass.