Chinese military chiefs believe a US Navy ship involved in a standoff near China's southern coast was on a spying mission, state media reported on Wednesday.
They also defended the actions of Chinese ships, which the Pentagon said had harassed and come dangerously close to the USNS Impeccable in the South China Sea, about 75 miles (120 kilometres) south of China's Hainan Island on Sunday.
"Top military officials lash out at US espionage," the English-language China Daily newspaper said in a front-page article.
"What was the ship doing? Anyone with eyes can see and our navy can see even more clearly," the paper quoted Vice Admiral Jin Mao, former vice commander of the navy, as saying.
"It's like a man with a criminal record wandering just outside the gate of a family home. When the host comes out to find out what he is doing there, the man complains that the host had violated his rights."
The paper also reported that Rear-Admiral Zhang Deshun, deputy chief-of-staff of the navy, had called the US vessel a spy ship, but it did not elaborate.
After the United States said overnight it would keep up its naval operations in international waters of the South China Sea, the Chinese foreign ministry issued a statement repeating its stance that the US Navy was in the wrong.
"China has lodged a solemn representation to the United States as the USNS Impeccable conducted activities in China's exclusive economic zone in the South China Sea without China's permission," ministry spokesman Ma Zhaoxu said.
"We demand that the United States take effective measures to prevent similar acts from happening," he said in a statement published on the ministry's website.
China has long expressed displeasure with US surveillance operations in waters it considers its "economic exclusion zone" and has had Chinese ships and planes approach US naval vessels in such areas in the past.
US intelligence director Dennis Blair said on Tuesday that the confrontation was the most serious military incident involving the two powers since a US spy plane collided with a Chinese fighter jet near Hainan island in April 2001.
The Chinese fighter pilot was killed.