The United States Congress, under the Taiwan Relations Act, requires the supply of weapons to the self-governing democracy for its defence.

US administrations had done so through sales rather than direct aid, but in August Washington for the first time approved direct US military aid to Taiwan under an assistance programme aimed at foreign governments.

"Despite China's firm opposition, the US government is determined to provide weapons to Taiwan... seriously harming China's sovereignty and security interests, and going further and further on the wrong and dangerous road of arming Taiwan," Chinese foreign ministry spokeswoman Mao Ning said at a regular press briefing.

She said that Lockheed Martin was the prime contractor in US arms sales to Taiwan that took place on August 24, and that Northrop Grumman had taken part in sales "many times".

"According to the Anti-Foreign Sanctions Law of the PRC, China has decided to impose sanctions on the above two US military companies," she said.

Mao said China urged the United States to stop selling weapons to Taiwan.

"Otherwise, it will inevitably face a resolute and strong response from China," she added.

The $80 million arms package approved in August was small compared with recent sales but was the first assistance to Taipei under the Foreign Military Financing programme, which generally involves grants or loans to sovereign countries.

China, an increasingly assertive diplomatic and military power, claims the self-ruled island of Taiwan as part of its territory and has vowed to seize it, by force if necessary.

In July, the United States unveiled a $345 million military aid package designed to quickly bolster the island's ability to deter a Chinese invasion.

The package -- which an official said featured intelligence, surveillance and reconnaissance equipment and small arms munitions -- was to be drawn from Washington's own reserves, allowing it to be delivered on a faster-than-usual timeline.

Friday's sanctions announcement comes after days of heightened tension in the region.

Taiwan's defence ministry said 68 Chinese aircraft and 10 naval vessels were detected near the island between Wednesday morning and Thursday morning.

Beijing has in recent years ratcheted up pressure on Taiwan.

The number of warplane flights around the island increased dramatically following last August's visit by Nancy Pelosi, then-speaker of the US House of Representatives.