China demands an apology from the U.S. side for taking a Chinese citizen "via abnormal means" into its embassy in Beijing, a Chinese Foreign Ministry spokesman said?in Beijing on?Wednesday.

Chen Guangcheng, a native of Yinan county in eastern China's Shandong province, entered the U.S. Embassy in Beijing in late April and left of his own volition after a six-day stay at the embassy, said Foreign Ministry spokesman Liu Weimin.

"It should be pointed out that Chen Guangcheng, a Chinese citizen, was taken by the U.S. side to the U.S. Embassy in Beijing via abnormal means, and the Chinese side is strongly dissatisfied with the move," Liu said.

He stressed that China demands that the United States thoroughly investigate the event, hold relevant people accountable and ensure that such an event does not happen again.

"What the U.S. side has done has interfered in the domestic affairs of China, and the Chinese side will never accept it," said the spokesman.

"The U.S. Embassy in Beijing has the obligation to observe relevant international laws and Chinese laws, and it should not do anything irrelevant to its function," said the spokesman.

China noted that the U.S. has expressed the importance it attaches to China's demands and concerns and has promised to take necessary measures to avoid similar events, he said.

The U.S. should reflect on its policies and methods and maintain the overall situation of Sino-U.S. bilateral ties with concrete acts, he said.

Liu said China is a country under rule of law, and its citizens' legitimate rights and interests are protected by the Constitution and laws.

"All citizens, at the same time, have the obligations to abide by the Constitution and laws," he said.