TAIPEI, March 26 (Reuters) - Taiwan and the United States have signed their first agreement under the Biden administration, the establishment of a Coast Guard Working Group to coordinate policy at a time when China's maritime actions have caused growing regional concern.

The new government of US President Joe Biden has moved to reassure Chinese-claimed Taiwan that its commitment to the island is rock solid, and has repeatedly expressed concern about China's efforts to pressure Taipei.

The Taiwanese representative to the United States, Hsiao Bi-khim, signed the agreement in Washington on Thursday (Mar 25), her office said in a statement.

Hsiao "emphasised that as a responsible stakeholder in the Indo-Pacific region, Taiwan is ready and willing to do more in the maritime domain", it added.

"It is our hope that with the new Coast Guard Working Group, both sides will forge a stronger partnership and jointly contribute even more to a Free and Open Indo-Pacific region."

Acting US Assistant Secretary of State for East Asian and Pacific Affairs Sung Kim was present at the signing ceremony, the statement said.

Taiwan is upgrading its coast guard with new ships, which can be drafted into naval service in the event of war, as the island deals with increasing encroachments from Chinese fishing boats and sand dredgers in Taiwan-controlled waters.

While the US, like most countries, has no formal diplomatic ties with Taiwan, it is the island's most important international backer and arms supplier.

China passed a law in January that for the first time explicitly allows its coast guard to fire on foreign vessels, which has caused concern regionally and in Washington.

China has defended the law as being in line with international practices and said that it is needed to safeguard the country's sovereignty, security and maritime rights.

Beijing also has maritime sovereignty disputes with Japan in the East China Sea and with several Southeast Asian countries in the South China Sea.