WASHINGTON: A US Navy nuclear submarine that was severely damaged in an accident while submerged in the disputed South China Sea last month struck an uncharted underwater mountain, the Navy said Monday.

The US Navy regularly conducts operations in the South China Sea to challenge China’s disputed territorial claims on small islands, reefs and outcrops, to the irritation of Beijing.

The 7th Fleet, which operates in the western Pacific, said an investigation had concluded that the USS Connecticut smashed into a geological formation and not another vessel on October 2.

“The investigation determined USS Connecticut grounded on an uncharted seamount while operating in international waters in the Indo-Pacific region,” a 7th Fleet spokesperson said in an emailed statement.

Beijing claims almost the entire South China Sea, parts of which are also claimed by four Southeast Asian countries as well as the self-ruled island of Taiwan.

The Navy confirmed the incident a week after it took place, only saying that Connecticut, a nuclear-powered fast-attack submarine, “struck an object while submerged.”

But Beijing on Tuesday accused Washington of failing to provide timely and detailed information on the incident, complaining of a “lack of transparency and lack of responsibility from the US.”

Foreign ministry spokesman Wang Wenbin said China urges the US to provide an explanation of the vessel’s “navigational intentions, the specific location of the accident, whether it was in the exclusive economic zone or territorial waters of any country, and whether it caused any nuclear leak or damage to the ocean environment.”

Washington should “stop sending warships and military aircraft to provoke trouble and make shows of force,” Wang said, warning that “this type of accident will only become more frequent” without any change in US actions.

The 7th Fleet said there would be further deliberation on “whether follow-on actions, including accountability, are appropriate.”

USNI News, published by the US Naval Institute, a think tank close to the Navy, reported that there were some moderate and minor injuries in the accident.

It said the crash damaged the sub’s forward ballast tanks and forced it to sail on the surface for a week back to Guam for repairs.

The ship’s nuclear plant was not damaged, the publication said.