BEIJING (REUTERS) - China's Foreign Ministry said on Thursday (May 21) it had lodged "solemn representations" with the United States to complain about a planned US sale of advanced torpedoes to Chinese-claimed Taiwan.

China firmly opposes US arms sales to Taiwan, ministry spokesman Zhao Lijian told a daily news briefing in Beijing.

The US government notified Congress of a possible sale of advanced torpedoes to Taiwan worth around US$180 million (S$254 million), further souring already tense ties between Washington and Beijing, which claims Taiwan as Chinese territory.

The United States, like most countries, has no official diplomatic ties with Taiwan, but is bound by law to provide the democratic island with the means to defend itself.

China routinely denounces US arms sales to Taiwan.

The US State Department approved a possible sale to Taiwan of 18 MK-48 Mod6 Advanced Technology Heavy Weight Torpedoes and related equipment on Wednesday.

"The Defence Security Cooperation Agency delivered the required certification notifying Congress of this possible sale today," it added.

The proposed sale serves US national, economic, and security interests by supporting Taiwan's "continuing efforts to modernise its armed forces and to maintain a credible defensive capability", the agency said.

The US announcement came on the same day Taiwan President Tsai Ing-wen was sworn in for her second term in office, saying she strongly rejected China's sovereignty claims. China responded that "reunification" was inevitable and that it would never tolerate Taiwan's independence.

China has stepped up its military drills near Taiwan since Tsai's re-election, flying fighter jets into the island's air space and sailing warships around Taiwan.

China views Tsai as a separatist bent on formal independence for Taiwan.

Tsai says Taiwan is an independent state called the Republic of China, its official name, and does not want to be part of the People's Republic of China governed by Beijing.