TAIPEI (REUTERS) - Senior national security officials from the United States and Taiwan have met to deepen cooperation, the government in Taipei said, with the first such meeting in four decades coming amid tense relations between the US and China.

Taiwan's national security chief David Lee met White House national security adviser John Bolton earlier this month, the island's foreign affairs ministry said in a statement last Saturday (May 25).

The official Central News Agency said the meeting was the first since the island and the US ended formal diplomatic ties in 1979.

China considers Taiwan a renegade province, to be reclaimed by force if necessary, and the meeting is likely to anger Beijing further, with Sino-US relations already tense.

The diplomatic temperature has risen in recent weeks amid an escalating trade war, US sanctions and China's increasingly muscular military posture in the South China Sea, where the US also conducts freedom-of-navigation patrols.

The rare meeting will be viewed by Taiwan as a sign of support from the Trump administration.

Tensions have also risen between Taipei and Beijing, which considers the democratically ruled island part of "one China".

The meeting took place during Mr Lee's May 13-21 visit to the US, Taiwan's brief statement said.

"During the trip, together with US government officials, Secretary-General Lee met with representatives from our diplomatic allies, reiterating support and commitment to a free and open Indo-Pacific region," the statement said.

Taiwan's foreign affairs ministry and America's de facto embassy in Taiwan declined to comment on Monday.

Beijing regularly calls Taiwan the most sensitive and important issue in ties with the US, which has no formal ties with Taiwan but is the island's main source of arms.

The US has in recent months increased the frequency of patrols through the strategic Taiwan Strait despite opposition from China.

China has been ramping up military and diplomatic pressure to assert its sovereignty over the island, conducting drills near Taiwan and snatching its few remaining diplomatic allies.

Earlier in May, the US House of Representatives backed legislation supporting Taiwan as members of the US Congress pushed for a sharper approach to relations with Beijing.

The Pentagon says Washington has sold Taipei more than US$15 billion (S$20.6 billion) in arms since 2010.