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

President Joe Biden's administration has recently announced a slew of arms sales to the island, including one that 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, without providing details of the curbs.

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.

- Arms sales -

The United States said in August that it had approved the sale to Taiwan of advanced sensor equipment -- built by Lockheed Martin -- for its fighter jets.

The systems improve warplanes' ability to detect airborne threats, increasing their chances of survival during combat.

The US State Department said at the time that the sale would help Taiwan "meet current and future threats by contributing to the recipient's abilities to defend its airspace, provide regional security and increase interoperability with the United States through its F-16 program".

The State Department said the F-16 Infrared Search and Track systems and related equipment would help Taiwan "maintain a credible defensive capability".

Another $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.

- Regional tensions -

Lockheed Martin previously faced sanctions imposed by Beijing after an arms deal in February 2022 involving $100 million in upgrades to Taiwan's US-built Patriot missile defence system.

Chinese foreign ministry spokesperson Wang Wenbin said at the time that the sanctions -- also targeting US defence firm Raytheon -- were intended "to safeguard China's sovereignty and security interests".

Lockheed Martin was also sanctioned by Beijing in 2020 due to its involvement in the sale of nearly $2 billion worth of missiles to Taiwan.

The fresh 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.