The Marshall Islands is one of 12 remaining nations that recognise Taiwan diplomatically after others jumped ship to China following promises of aid and investment.

Taiwan calls itself a sovereign nation, but Beijing insists the island is part of its territory and opposes any official exchanges with it.

Beijing has sought to push Taipei off the international stage by poaching its allies and blocking it from global forums, including the United Nations.

Marshall Islands President Hilda Heine expressed her government's commitment to "remain a staunch ally" of Taiwan, after Lai arrived in the capital Majuro, where the Taiwanese leader held talks with the government and attended a banquet.

"Taiwan and the Marshall Islands share a traditional Austronesian culture as well as the values of freedom and democracy," Lai told Heine, speaking through an interpreter.

Lai's first overseas trip since taking office in May began with a two-day visit to the United States where he discussed "China's military threats" towards Taiwan during a call with former US House speaker Nancy Pelosi, and met with US government officials and members of Congress -- drawing a fresh barrage of criticism from Beijing.

China rejects any international recognition of Taiwan and especially bristles at official contact between the island and Washington, Taiwan's most important security backer.

China on Tuesday vowed to defend its "national sovereignty" and "territorial integrity" as Lai visited the Marshall Islands.

"The Taiwan issue is the core of China's core interests," foreign ministry spokesman Lin Jian said, when asked whether Beijing could launch another round of war games around the self-ruled island in response to the Pacific tour.

After the Marshall Islands, Lai will visit Taiwan's other remaining Pacific island allies Tuvalu and Palau as well as stop for one night in the US territory of Guam.

The Marshall Islands, a sprawling chain of volcanic islands and coral atolls halfway between Hawaii and Australia, has a long-standing agreement with the United States that gives it security and budget guarantees.

In return, the US military has access to its territory.

"We are like family, and we are also close partners who support each other," Lai told Heine.

"Over many years of mutual support, we have provided one another the greatest possible backing."

During his visit, Lai announced Taiwan would provide a "preferential loan" for state-owned Air Marshall Islands to purchase new aircraft.

Taiwan, which has a long history of providing development finance in the Pacific, will also help build a pig slaughterhouse in 2025 to improve "food security" in the Marshall Islands, Lai said.

Lai said Taiwan would look at how to help the Marshall Islands address "national security issues that are important to President Heine", without elaborating.

Heine told Lai that the Pacific island nation would "remain a staunch ally and continue to voice and support Taiwan's inclusion in the United Nations and all other regional and international organisations."

- 'Long-time friends' -

China has fumed over recent US arms sales to Taiwan and Lai's stop in the US island state of Hawaii, where he was welcomed with red carpets and garlands of flowers.

Pelosi's long-standing support for Taiwan has infuriated China, which responded to her visit to Taipei in 2022 with massive military drills around the island.

Lai and Pelosi discussed "China's military threats toward Taiwan", presidential spokeswoman Karen Kuo told reporters in Hawaii, describing the 20-minute call between the "long-time friends" as "warm and amicable".

In response to Lai's conversation with Pelosi, China on Monday called on the United States to "stop meddling with Taiwan" and cease "supporting and indulging Taiwan independence separatist forces".

Taiwan faces the constant threat of a military attack by China, which regularly deploys fighter jets and warships around the island to press its claims, and Beijing has not ruled out using force to bring the island under its control.

China and Taiwan have been governed separately since 1949, when Chiang Kai-shek's nationalist forces were defeated by Mao Zedong's communist fighters and fled to the island.

In his first public speech of the trip on US soil, Lai said Saturday there was a need to "fight together to prevent war", warning there were "no winners" from conflict.

On the eve of Lai's week-long Pacific tour, the United States approved a proposed sale to Taiwan of spare parts for F-16s and radar systems, as well as communications equipment, in deals valued at $385 million in total.