China protest probed

50 surround U.S. ambassador’s car outside embassy. Visiting Panetta stays out of isle dispute.

BEIJING — China said Wednesday it was investigating an incident where about 50 protesters surrounded the car of the U.S. ambassador, tried to block him from entering the embassy compound and ripped the car’s flag.

Chinese police cleared roadblocks and some Japanese businesses reopened after days of large, sometimes violent protests in many cities over Japan’s recent purchase of islands also claimed by Beijing.

In Beijing, the bitterness spilled over from the Japanese Embassy to the nearby U.S. Embassy.

U.S. Ambassador Gary Locke told reporters Wednesday that Chinese authorities were “very quick” to move the demonstrators away. Video posted on YouTube showed a small number of protesters throwing small objects at the car before Chinese security forces moved in to break up the crowd. “It was all over in a matter of minutes, and I never felt in any danger,” Locke said.

The U.S., a close ally of Japan, has said it is staying out of the dispute over the islands.

The incident came amid heightened vigilance for American diplomats after violent attacks on U.S. embassies in Libya, Yemen and Egypt. The embassy said it has asked China’s government to do everything possible to protect American facilities and personnel.

State Department spokeswoman Victoria Nuland said the U.S. has registered its concern with China both in Washington and Beijing, and Chinese authorities have expressed regret over the incident.

Nuland said the preliminary U.S. assessment was that the car was “a target of opportunity” for protesters who had gathered outside the nearby Japanese Embassy.

Chinese Foreign Ministry spokesman Hong Lei told a regular news briefing Wednesday that the incident was “an individual case,” but that China was investigating it.

The protests over the weekend were triggered by the Japanese government’s decision last week to purchase some disputed East China Sea islands from their private Japanese owners. More demonstrations followed Tuesday, the 81st anniversary of Japan’s invasion of China, an emotional remembrance that further stoked the outrage.

China’s future leader, Xi Jinping, told visiting U.S. Defense Secretary Leon Panetta on Wednesday that Japan’s purchase of the islands was a farce, according to the official Xinhua News Agency.

NG HAN GUAN / AP Chinese paramilitary police march with their shields outside the entrance to the Japanese Embassy in Beijing, China, on Wednesday. People across China have engaged in days of furious protests over disputed East China Sea islands.

LARRY DOWNING / NEW YORK TIMES Cadets listen to U.S. Secretary of Defense Leon Panetta speak at the Armored Forces Engineering Academy in Beijing on Wednesday.