China accused the US on Tuesday of “illegal” intrusion into its exclusive economic zone in a spat that could torpedo the two countries’ efforts to improve their military relationship following months of disruption.

The US navy surveillance ship Impeccable had “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.