BEIJING — A car carrying the US ambassador to China was slightly damaged after becoming the target of boisterous anti-Japan demonstrators who were expressing outrage over a territorial dispute and marking the 81st anniversary Tuesday of Japan’s invasion of China.

The State Department said in a statement Wednesday that Ambassador Gary Locke was unhurt, and that diplomats have expressed concerns to the Chinese Foreign Ministry.

The statement said around 50 protesters surrounded Locke’s car as he tried to enter the embassy and were eventually removed by Chinese security personnel.

The event comes amid heightened vigilance for American diplomats following violent attacks on US embassies in Libya, Yemen, and Egypt. The statement said embassy officials have asked the Chinese government to do everything possible to protect American facilities and personnel.

People across China have engaged in days of protests over some East China Sea islands, claimed by Beijing and Tokyo, that Japan purchased last week from a private owner. The United States has said it is staying out of the dispute.