The US Navy revealed on Thursday that the USS Connecticut, a Seawolf class fast-attack submarine, had "struck an object while submerged" on October 2 in international waters in the Indo-Pacific region.

The US official, speaking on condition of anonymity, declined to give the precise location where the incident occurred but said it happened in the South China Sea.

Eleven sailors were injured including two moderately.

The official declined to reveal the depth at which the collision occurred, citing "operational security."

An investigation would be conducted to determine the cause.

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

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.

Chinese Foreign Ministry spokesman Zhao Lijian said Friday that Beijing was "extremely concerned" about the collision and accused the United States of deliberately concealing the nature of the incident.

Washington should provide "detailed clarification" of the event, including information about what the sub collided with, whether it caused nuclear leakage and whether it damaged the local marine environment, Zhao said.

The spokesman accused the United States of long "disturbing the peace" in the South China Sea "under the banner of freedom of navigation."

The US Navy said meanwhile that two strike groups led by its aircraft carriers USS Ronald Reagan and USS Carl Vinson had carried out joint operations with other nations in the Philippine Sea on October 3.

The US warships were joined by the JS Ise, a Japanese Hyuga-class helicopter destroyer, and Britain's HMS Queen Elizabeth, the US Navy said in a statement.

"The integrated at-sea operations brought together more than 15,000 sailors across six nations and demonstrates the US Navy's ability to work closely with its unmatched network of alliances and partnerships in support of a free and open Indo-Pacific," it said.