Esper landed at Osan Air Base in Pyeongtaek, 70 kilometers south of Seoul, from Mongolia for a two-day visit as part of his five-nation tour of the Asia-Pacific region, which includes stops in Australia, New Zealand and Japan, according to defense ministry officials. It is his first overseas trip since taking office last month.

On Friday, he plans to meet with Jeong to discuss pending issues, including "ways to boost cooperation for the denuclearization of the Korean Peninsula and the condition-based transfer of the wartime operational control," Jeong's office said in a release.

After the talks, the two sides are expected to publicly release details on the Seoul-Washington combined military exercise, including its name and duration.

The allies practically kicked off their summertime combined exercise on Monday, though neither side has officially confirmed its commencement in apparent consideration of North Korea, which has sent strong warnings repeatedly against the exercise by launching short-range missiles.

The command post exercise is meant to test South Korea's initial operational capability for the envisioned OPCON transfer from Washington to Seoul, according to the officials.

The two chiefs are to share their assessment of North Korea's newly-developed short-range ballistic missiles, known as KN-23, and discuss ways to better counter its evolving missile threats, they added.

During his visit, Esper is also likely to reiterate US support for the General Security of Military Information Agreement, the military information-sharing pact between Seoul and

Tokyo, as a key trilateral security mechanism, due to the possibility of its abrogation amid a trade and diplomatic row between the two countries.

Also drawing attention is whether tough and sensitive issues will also be on the table, including Seoul's possible participation in the US-led coalition to safeguard the Strait of Hormuz off Iran amid heightened tensions between Washington and Tehran.

The US is struggling to drum up support for its efforts to counter Iranian activities in the strategically crucial sea lane, and South Korea is known to have been reviewing various options, though no formal requests regarding the matter have been received.

Esper's visit also comes as the US is calling on Seoul to pay more for the upkeep of the 28,500-strong US Forces Korea. While President Donald Trump tweeted Wednesday that the two nations have begun talks on the issue, the foreign ministry here said their official negotiation has yet to be launched.

The issue of the defense payment may be discussed during Esper's planned meeting with Foreign Minister Kang Kyung-wha on Friday ahead of his talks with Minister Jeong, according to sources.

Regarding the defense cost-sharing talks, a foreign ministry official in Seoul said the two countries have exchanged only "broad-brush views" on the issue without discussing details.

"Only after the negotiations begin will we be able to talk about a raise or the background," the official told reporters when asked if the two sides have discussed the issue even unofficially.

"They have yet to set up their negotiating team too. We should start forming the teams and then decide when to meet for the first round of talks, but nothing (has taken place)."

The defense chief is also expected to pay a courtesy call on President Moon Jae-in before leaving South Korea, they added. Esper, who served as the secretary of the Army, was sworn in as the 27th Secretary of Defense in July after seven months of turmoil surrounding the top job at the Pentagon since James Mattis resigned from the post in December. (Yonhap)