Two US lawmakers met Taiwanese president-elect Lai Ching-te on Thursday to reaffirm Washington's support for the self-ruled island, which China claims as part of its territory. 

Lai won the 13 January poll despite warnings from Beijing that he would bring "war and decline" to Taiwan, securing a third term for the Democratic Progressive Party that rejects China's claim to the island. 

Democrat Ami Bera of California and Florida Republican Mario Diaz-Balart arrived in Taipei on Wednesday in their roles as co-chairs of the Congressional Taiwan Caucus. They are expected to stay until Friday.

"Among the main messages we are bringing here today... is that the support of the United States for Taiwan is firm, it's real and it's 100 percent bipartisan," Diaz-Balart said in a meeting with Lai. 

Lai, who is Taiwan's current vice president, thanked them for showing their support via "concrete action".

"Your visit at this important juncture fully demonstrates the US' rock-solid support of Taiwan."

He said he hoped the US Congress would "continue to support Taiwan in bolstering our self-defence capabilities so that we can jointly safeguard regional peace, stability and prosperity".

Bera and Diaz-Balart represent the second US group to arrive since Taiwan's closely watched presidential election.   

The first was an unofficial delegation sent by President Joe Biden to congratulate Lai two days after the vote.

But that visit was overshadowed by Pacific nation Nauru abruptly announcing it was switching allegiance to Beijing, leaving Taipei with just 12 remaining diplomatic allies. 

While the United States recognises Beijing over Taiwan, it is a key partner of the island and a major weapons provider. 

Speaking to President Tsai Ing-wen after meeting Lai, Diaz-Balart said it was "a challenging time". 

"We see what is coming... out of Beijing, and their level of aggression both here across the strait and across the region," he said. 

"As democracies, as people who believe in freedom, it is incumbent on us to address these aggressions."

'Negative words and deeds'

China has never renounced the use of force to try and bring Taiwan under its control and has maintained a near-daily military presence around the island. 

On Wednesday, 18 Chinese warplanes, six naval vessels, and three Chinese balloons were detected around Taiwan, according to Taipei's defence ministry.

On the same day, a US warship sailed southward through the Taiwan Strait, a sensitive waterway separating the island from China, the US Navy said in a statement.

"(The USS John Finn's) transit through the Taiwan Strait demonstrates the United States' commitment to upholding freedom of navigation for all nations as a principle," it said. 

"No member of the international community should be intimidated or coerced into giving up their rights and freedoms."

In Beijing, the foreign ministry complained Thursday that Washington had "carried out a series of negative words and deeds" since Lai's election.

Spokesman Wang Wenbin urged the United States to "immediately stop infringing and provocative actions" and "stop causing trouble for peace and stability across the Taiwan Strait".