BANGKOK (AFP) - The US and 10 South-east Asian states will hold their first joint maritime exercises in September, aimed at preventing "wrongdoing" as Washington and Beijing jostle for influence in the region.

Washington has traditionally been the dominant naval power in South-east Asia and its re-engagement with the area comes as a deteriorating trade war with China threatens to engulf the global economy.

US Secretary of State Mike Pompeo attended a regional summit earlier this month with the 10-country Association of South-east Asian Nations (Asean) in a bid to promote the Trump administration's so-called "Indo-Pacific" strategy.

Also a source of friction is China's expansive claims to the South China Sea, as the resource-rich waters contain some of the world's most vital commercial shipping lanes.

Despite having conflicting interests with four rival claimants in Asean, China last year held a joint maritime drill with the regional bloc.

The navies of the US and Asean will do the same on September 2, the US embassy in Bangkok announced late Friday (Aug 23), with the exercises launching at a Thai naval base in Chonburi province east of Bangkok.

The purpose of the five-day maritime drill is to "maintain maritime security, focus on prevention and pre-empt wrongdoing in the sea", said a US embassy statement.

The drills will primarily take place off the coast of Vietnam's southernmost Ca Mau province, where the US Navy will dispatch "suspicious boats" in a mock exercise to help Asean's navies to "search, verify and legally prosecute" the boats.

Tensions between China and Vietnam have been high since July in the disputed sea when a Chinese survey ship entered waters where Hanoi has several oil and gas projects.

The ship left for a brief period this month, and then came back - prompting calls from Hanoi to vacate the area.

But a Thai defence ministry spokesman on Saturday played down the timing of the US-Asean drills.

"We held exercises with China, now we are having exercises with the US... it has nothing to do with the current situation," said Lieutenant General Kongcheep Tantravanich.

On Friday, a US military ship sailed through the Taiwan Strait to conduct a "freedom of navigation" voyage, the island's defence ministry said.

The move is likely to further irk China in the wake of Washington's latest US$8 billion (S$11.1 billion) arms sales to self-ruling Taiwan, which Beijing views as part of its territory.