Taipei, Taiwan - A visit by two US senators to Taiwan drew the ire of Beijing, who accused the US of undermining China's sovereignty.

Republican senators Roger Wicker and Deb Fischer arrived in Taipei on Friday for a two-day visit, as President Donald Trump seeks to strike a trade deal with China, who insists that Taiwan is part of its territory.

Wicker, who heads the US Senate armed services committee, said on Friday that he was determined that the United States and Taiwan remain "the best of friends," ahead of a trip this weekend.

He added that he and Fischer wanted to reiterate to Taiwan "our determination to remain the best of friends and to defend the freedom of everyone and both of our great countries."

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"It is our determination and our intention that Taiwan remain free and make its own decisions," Wicker said after talks with Taiwanese President Lai Ching-te.

"Part of maintaining the freedoms that we have is enhanced cooperation militarily, enhanced cooperation with our defense industrial base, making the best use of those funds."

Fischer said the Senate understands "the gravity of the challenges that Taiwan faces" and that a "stronger Taiwan means a stronger United States and vice versa."

Ahead of the meeting with Wicker and Fischer, Lai said that he hoped Taiwan and the US will further "enhance cooperation," and insisted that Taipei and Beijing were "not subordinate" to each other.

China's Foreign Ministry Spokesperson Guo Jiakun slammed the decision by Senators Wicker and Fischer to conduct a friendly visit to Taiwan as a violation of China's sovereignty and referred to Lai's government as "separatist forces."

The US is Taipei's most important backer and biggest supplier of arms.

The island nation has remained separate from China since 1949, when the Chinese Nationalist Party Kuomintang fled to Taiwan after Mao Zedong's Communist Party claimed power in Beijing.

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"China firmly opposes any form of official interactions between the US and China's Taiwan region," Guo said during a daily press conference on Friday.

"The visit by the US Congress member seriously violated the one-China principle and the three China-US joint communiqués, harmed China's sovereignty and territorial integrity, and sent a seriously wrong message to 'Taiwan independence' separatist forces," he said.

"China strongly deplores that," Guo said. "There is but one China in the world, and Taiwan is an inalienable part of China's territory."

"Stop interfering in China's internal affairs and abetting and supporting 'Taiwan independence' separatist forces under any pretext, stop official interactions with China's Taiwan region, and stop creating tensions for the situation across the Taiwan Strait."