TAIPEI/BEIJING - The United States has cleared a sale of advanced Patriot air defence missiles to Taiwan despite opposition from rival China, where a military official proposed sanctioning U.S. firms that sell arms to the island.

The U.S. defence department announced the contract late on Wednesday, allowing Lockheed Martin Corp to sell an unspecified number of Patriots, Washington's de facto embassy in Taipei said.

The hardware, some of the best in its class, could shoot down Chinese short-range and mid-range missiles, defence analysts say.

The sale rounds out a US$6.5-billion (S$9.087 billion) arms package approved under then U.S. President George W. Bush in late 2008, said Wendell Minnick, Asia bureau chief with Defense News.

"This is the last piece that Taiwan has been waiting on," Minnick said.

China has urged the United States to cancel any planned arms sales to Taiwan to avoid damaging ties with Beijing, and a Chinese Foreign Ministry spokeswoman, Jiang Yu, swiftly denounced the missile deal.

"We have already made stern representations to the U.S. side, and we have urged the United States to clearly recognise the serious harm caused by arms sales to Taiwan," Jiang told a regular news conference in Beijing.

Meanwhile, Chinese Vice Admiral Yang Yi told the China News Service that though developing good ties between China and the United States was important, some things could not be accepted. "You can't just be forebearing and conciliatory when it comes to the development of stable and healthy Sino-U.S. relations, and especially when it comes to a question of principles you should never blindly make concessions," he said.

Some U.S. companies which sell weapons to Taiwan also want to sell aircraft and other goods to China, added Yang, who is also a researcher at the Chinese National Defence University's Strategic Studies Institute, without naming any firms.

"Why don't we take defensive countermeasures against them? Apart from just protesting to the U.S. government and taking necessary steps, why don't we put sanctions on these troublemakers?"

China has claimed sovereignty over self-ruled Taiwan since 1949, when Mao Zedong's Communists won the Chinese civil war and Chiang Kai-shek's Nationalists fled to the island. Beijing has vowed to bring Taiwan under its rule, by force if necessary.

The United States switched diplomatic recognition from Taipei to Beijing in 1979, recognising "one China". But it remains Taiwan's biggest ally and is obligated by the 1979 Taiwan Relations Act to help in the island's defence.

"Taiwan's defence ministry looks favourably at the U.S. continuing to sell Taiwan weapons for its self defence," Taiwan military spokesman Martin Yu said. Taiwan estimates China is aiming 1,000 to 1,500 missiles at the island.