Eric Holcomb, the Republican governor of the US state of Indiana, began a four-day visit to Taiwan Monday.

Holcomb met with Taiwan's President Tsai Ing-wen who told him the US and Taiwan are key security and economic allies.

"Taiwan has been confronted by military threats from China, in and around the Taiwan Strait," Tsai told Holcomb during the meeting at her office in Taipei.

"At this moment, democratic allies must stand together and boost cooperation across all areas," Tsai added.

The focus of Holcomb's visit is on economic exchange, particularly in the critical area of semiconductors.

His is the third high-profile visit from US politicians in recent weeks, and like the others, it will likely draw rebukes and condemnation from Beijing.

What is the backdrop to Holcomb's visit?Holcomb's visit comes at a tense moment for Taiwan, China and the US after House Speaker Nancy Pelosi visited Taiwan earlier this month.

Pelosi was the highest-level member of the US government to visit Taiwan, which Beijing views as part of its territory, in 25 years.

Taiwan rejects Beijing's territorial claims and remains democratic and self-governing.

China's People's Liberation Army held several days of snap exercises following Pelosi's visit, forcing Taipei to reroute and cancel flights. Chinese warplanes were also sent to probe across the Strait of Taiwan.

China also reacted with visa bans and sanctions on Taiwanese figures, though the effects are unclear.

Beijing accuses the US of encouraging the island's independence through the sale of weapons and engagement between US politicians and the island's government.

Holcomb is scheduled to visit South Korea next.