It's unclear what the Seawolf-class submarine may have hit while it was submerged

Expressing grave concern over a US nuclear-powered submarine sustaining damage in the disputed South China Sea, China on Friday demanded Washington to reveal the details and the location of the accident and blamed America's frequent air and naval sorties in the Indo-Pacific to assert the "freedom of navigation" as the "root cause" of the incident.

The USS Connecticut struck an object underwater in the South China Sea (SCS) on Saturday. Eleven sailors on board the submarine were injured in the accident. None of the injuries were life-threatening, a statement from the US Pacific Fleet said on Thursday.

It's unclear what the Seawolf-class submarine may have hit while it was submerged.

"The submarine remains in a safe and stable condition. USS Connecticut's nuclear propulsion plant and spaces were not affected and remain fully operational," the US Navy statement said.

Asked for his reaction, Chinese Foreign Ministry spokesman Zhao Lijian told a media briefing here that “China is gravely concerned about the incident”.

"As the party involved, the US should clarify in specific details what happened, including the exact location of the incident, the US side's navigation intention, the details of the incident, the object the submarine struck, whether the collision caused a nuclear leak or damaged local marine environment, etc," Zhao said.

He alleged that the US has long been making trouble in the South China Sea in the name of "freedom of navigation", which poses a grave threat and major risks for regional peace and stability.

"This is the root cause of this incident," he said.

The US has been periodically sending its naval and air patrols through the South China Sea, challenging China's claims of sovereignty over the area and also asserting the freedom of navigation.

Zhao said the US has deliberately stalled and concealed the specifics of the incident. It lacks transparency and responsibility, he said.

"China and other countries surrounding the South China Sea cannot help but ask what truly happened and what the US' intention is," he said.

The spokesman also used the opportunity to criticise the AUKUS security alliance announced by the US, Britain and Australia. The trilateral alliance - widely seen as an effort to counter China's influence in the contested South China Sea - was announced by US President Joe Biden, UK Prime Minister Boris Johnson and his Australian counterpart Scott Morrison last month.

Zhao pointed out that the US and the UK recently decided to conduct nuclear submarine cooperation with Australia, a non-nuclear weapon state, and proliferate nuclear submarines in the Asia-Pacific.

"This is bound to create nuclear proliferation risks, spark an arms race and undermine efforts to establish a Southeast Asia nuclear-free-zone. The odds of a nuclear incident will also increase dramatically.

"The US should abandon the obsolete Cold War zero-sum mentality and narrow geopolitical notions and stop such erroneous practice that undermine regional peace, stability and development," the Chinese foreign ministry spokesman said.

China claims most of the SCS. The Philippines, Vietnam, Malaysia, Brunei and Taiwan have counterclaims over the area. Over the years, China has built a number of military installations in the reclaimed islands in the SCS and deployed a big fleet of its naval ships and submarines.

At the briefing, China also asked the US to sever defence and official ties with Taiwan while reacting to reports that US troops were training Taiwanese troops. He also asked the US to sever military and official ties with Taiwan, while reacting to reports that a small number of US special operations forces were deployed in Taiwan on rotational basis to train Taiwanese forces.

Reports quoted a Pentagon spokesman John Supple as highlighting that the US support for defence relationship with Taiwan “remains aligned against the current threat posed by the People's Republic of China."

China views Taiwan as a breakaway province. However, democratic Taiwan sees itself as a sovereign state. Beijing has not ruled out the possible use of force to achieve unification with Taiwan.

The One China principle which emphasises that Taiwan is part of China is the political foundation for China-US ties, Zhao said.

“The US must sever diplomatic relations with Taiwan and abrogate its mutual defence treaty with Taiwan and must withdraw” from the estranged island, he said.

The US should fully recognise the "highly sensitive nature" of Taiwan-related issues and the "gravely detrimental nature" of relevant issues, abide by the one-China principle and the three China-US joint communiques, and stop arms sales to and military ties with Taiwan to avoid seriously damaging China-US relations and peace and stability across the Taiwan Strait.

"China will take all necessary measures to defend its sovereignty and territorial integrity," Zhao said.

The US should only stick to the commitments to maintain cultural, commercial and other unofficial relations with the people of Taiwan, he said. Tensions flared up between China and Taiwan as the Chinese military flew a record 150 air force jets into Taiwan's Air Defence Identification Zone during the week-long holidays to celebrate China's National Day on October 1.

The Taiwan issue figured in Wednesday's talks between top Chinese diplomat Yang Jiechi and US National Security Advisor Jake Sullivan in Zurich during which the two sides have agreed to improve the strained ties.

The intensity of China's air raids prompted US President Joe Biden to remind his Chinese counterpart Xi Jinping that they have agreed to abide by the “Taiwan agreement” during their telephone talks last month.

"I've spoken with Xi about Taiwan. We agree ... we'll abide by the Taiwan agreement. We made it clear that I don't think he should be doing anything other than abiding by the agreement," Biden had earlier said.