The US government has approved the possible sale to Saudi Arabia of an advanced missile defence system worth $15bn, the Pentagon said.

The Terminal High Altitude Area Defence (THAAD), which has already been supplied to Saudi Arabia's neighbours Qatar and the United Arab Emirates, is one of the most capable anti-missile batteries in the US arsenal and comes equipped with an advanced radar system.

Saudi Arabia had asked to buy 44 THAAD launchers and 360 missiles, as well as fire control stations and radars.

"This sale furthers US national security and foreign policy interests, and supports the long-term security of Saudi Arabia and the Gulf region in the face of Iranian and other regional threats," the Pentagon's Defense Security Cooperation agency said in a statement on Friday.

The sale can go ahead if the US Congress does not object within 30 days.

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THAAD's recent deployment by the US military in South Korea to protect against a possible North Korean attack drew protests from Beijing, who feared its sensors would be able to penetrate into Chinese airspace and upset the balance of power.

But the state department said it would advise Congress that, in Saudi hands, the system would act to stabilise the situation in the Gulf and help defend US forces in the region and their allies.

"The proposed sale of this equipment and support will not alter the basic military balance in the region," it said.

Aerospace giant Lockheed Martin Co is the prime contractor for the THAAD system, with defence contractor Raytheon Co playing an important role in its deployment.