The US navy surveillance ship Impeccablehad “moved about in China's EEZ in the South China Sea without approval from China”, said Ma Zhaoxu, a foreign ministry spokesman. He said that was in violation of the United Nations Convention on the Law of the Sea and Chinese laws and regulations but refused to specify which legal requirements had been violated.

The Pentagon said on Monday that the US naval ships were permitted to operate inside the Chinese exclusive economic zone, adding that “coastal states do not have a right under international law to regulate foreign military activities in the EEZ”.

The accusation came in response to a complaint by the US government on Monday that Chinese coastguard vessels, fishing trawlers and naval vessels had harassed theImpeccableon Sunday, 75 miles south of the Chinese island of Hainan, in international waters.