Esper will depart Wednesday to travel to Seoul, Bangkok, Manila and Hanoi, Pentagon spokesman Jonathan Hoffman said during a press briefing. He did not provide the exact dates, but it appears likely the secretary will travel in that order.

Esper's trip to Seoul comes ahead of the Nov. 23 expiration of the General Security of Military Information Agreement between South Korea and Japan.

Washington has urged Seoul to reconsider its decision to end the pact in consideration of the three countries' mutual security interests.

This week, US Assistant Secretary of State for East Asian and Pacific Affairs David Stilwell was also in Seoul to apparently urge the pact's renewal.

Hoffman said he can "practically guarantee" the topic will be part of Esper's conversations in Seoul next week.

"We're hopeful. We're optimistic. We're going to continue to push on," Hoffman said. "It's something that we would like to see resolved, so that all of us can focus on the biggest threats in the region, which is North Korea's activities and then, the Chinese efforts to destabilize the region."

The US views GSOMIA as a key platform for trilateral cooperation against security threats from North Korea and China.

Despite US opposition, South Korea announced in August that it will terminate the deal amid heightened tensions with Japan over trade and wartime history.

"We've tried to work around some of this with regard to being able to do some of the bilateral information-sharing between each of us to try to keep going through," Hoffman said.

In a press release, the Pentagon added that the defense secretary will attend the 51st US-Republic of Korea Security Consultative Meeting, where he will meet with South Korean Defense Minister Jeong Kyeong-doo and other senior South Korean officials.

The two sides will "discuss the Alliance and reaffirm our commitment to enhancing our bilateral defense cooperation to address issues of mutual importance to the security and stability of the Korean Peninsula and the Indo-Pacific region," the release said.

It will be Esper's second visit to Seoul since assuming office. The first visit was in August.

The allies have faced a number of challenges in recent months, including ongoing negotiations to renew a cost-sharing deal for the upkeep of 28,500 American troops stationed in the South.

US President Donald Trump has made clear he expects Seoul to hike its share, with reports suggesting Washington seeks a more than fivefold increase to US$5 billion next year.

In Bangkok, Esper will attend the ASEAN Defense Ministers' Meeting Plus and meet with allies and partners in the region who "share a vision for a free and open Indo-Pacific," according to Hoffman. (Yonhap)