The US State Department has approved the potential sale of spare parts for F-16 jets and radars to Taiwan for an estimated $385 million, the Pentagon said on Friday, a day before Taiwan President Lai Ching-te starts a sensitive Pacific trip.

The United States is bound by law to provide Chinese-claimed Taiwan with the means to defend itself despite the lack of formal diplomatic ties between Washington and Taipei, to the constant anger of Beijing.

Democratically governed Taiwan rejects China’s claims of sovereignty.

China has been stepping up military pressure against Taiwan, including two rounds of war games this year, and security sources have told Reuters that Beijing may hold more to coincide with Lai's tour of the Pacific, which includes stopovers in Hawaii and Guam, a US territory.

The Pentagon’s Defense Security Cooperation Agency said the sale consisted of $320 million in spare parts and support for F-16 fighters and Active Electronically Scanned Array Radars and related equipment.

The State Department also approved the potential sale to Taiwan of improved mobile subscriber equipment and support for an estimated $65 million, the Pentagon said. The principal contractor for the $65 million sale is General Dynamics (GD N).

Taiwan’s defence ministry said it expected the sales to “take effect” within a month and that the equipment will help maintain the F-16 fleet's readiness and “build up a credible defence force.”

“Taiwan and the United States will continue to strengthen their security partnership and work together to maintain peace and stability in the Taiwan Strait and the Indo-Pacific region,” it said in a statement.

Last month, the United States announced a potential $2 billion arms sale package to Taiwan, including the delivery for the first time to the island of an advanced air defense missile system battle tested in Ukraine.

Lai leaves for Hawaii on Saturday on what is officially a stopover on the way to Marshall Islands, Tuvalu and Palau, three of the 12 countries that still to have formal diplomatic ties with Taipei. He will also stop over in Guam.

Hawaii and Guam are home to major US military bases.

China on Friday urged the United States to exercise “utmost caution” in its relations with Taiwan.

The State Department said it saw no justification for what it called a private, routine and unofficial transit by Lai to be used as a pretext for provocation.