Pentagon chief Chuck Hagel meets with his Asian counterparts on Wednesday as the US promotes its shift to the region, but a potential showdown with Syria looms over the talks.

Hagel plans to call for restraint in the disputed South China Sea and underscore America's strategic tilt to the Asia-Pacific at the gathering in Brunei of defense ministers from the Association of Southeast Asian Nations (ASEAN), China and elsewhere, officials said.

The two-day ASEAN meeting is the main event of Hagel's week-long trip to Southeast Asia but a mounting crisis between Syria and the West has repeatedly demanded his attention.

"We are ready to go, like that," Hagel told the BBC in an interview Tuesday, when asked about preparations for potential military action against Syria.

The confrontation with Syria over the regime's alleged use of chemical weapons has illustrated the challenges faced by Washington's much-touted "rebalance" towards the Asia-Pacific.

Turmoil in the Middle East has repeatedly overshadowed the Obama administration's bid to bolster trade and military ties with economically vital Asia.

Despite Pentagon budget cuts, US officials say Washington will stick by plans to deploy more ships and troops to the region while offering training and hardware to countries anxious about China's growing military reach.

"To be relevant to the security issues in the region, you need to be present," said a US defence official who spoke on condition of anonymity.

Hagel is due to hold talks with his counterparts from Japan, South Korea, Vietnam and Brunei on the sidelines of the ASEAN gathering Wednesday.

He also will meet China's defence minister, General Chang Wanquan, and Myanmar's defence chief.

Tense territorial disputes in the South China Sea and elsewhere will be a key focus of the talks, officials said.

Hagel has renewed US calls for the adoption of a code of conduct at sea to prevent potential clashes.

China has been accused of dragging its feet on discussing the issue with ASEAN but this year said it would enter into future talks on the matter.

The Pentagon is offering ships, radar and other security assistance to countries in Southeast Asia, partly as a counterbalance to China's military build-up.

On Tuesday, Hagel announced the sale of eight Apache helicopters to Indonesia during a visit to Jakarta.

The United States, however, has to tread carefully on China during the trip and officials said Washington wanted to avoid inflaming tensions in the region.

"In no case do we ask countries to choose between us and China," said the defence official.

Hagel is also expected to discuss the threat posed by North Korea's nuclear weapons and missile program with Chang as well as ministers from Japan and South Korea. (AFP)