The United States and South Korea will begin negotiating this week a new cost-sharing agreement for basing U.S. troops in South Korea, Seoul said Monday.

“The two sides will discuss to produce a reasonable pact that can help strengthen the joint defense readiness of South Korea and the U.S. and be accepted by our people," the South Korean Foreign Ministry said, according to Yonhap news agency.

The negotiations come at a critical time for the alliance, with North Korea making rapid progress on its nuclear and missile programs. President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE has spoken about wanting South Korea to take on a greater share of the cost of deploying U.S. troops there.

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Under a cost-sharing deal reached in 2014, Seoul paid $867 million toward U.S. military costs that year, and its share has risen each year based on inflation. This year, South Korea is paying about $890 million, a little less than half of the total.

The current deal, the ninth since 1991, expires Dec. 31. The first round of negotiations for the 10th deal will take place Wednesday through Friday in Honolulu, according to the foreign ministry.

South Korean negotiators will be led by career diplomat Chang Won-sam, appointed by South Korean President Moon Jae-in in mid-November in anticipation of tough negotiations. The United States team will be led by Timothy Betts, acting deputy assistant secretary of State for plans, programs and operations.

The United States has about 28,500 troops stationed in South Korea.

During the presidential campaign, Trump said he would be willing to withdraw U.S. troops stationed in the country if South Korea didn’t pay a bigger share of the cost of the deployment.

He has softened his rhetoric since taking office, though the cost issue has still reportedly come up in Trump’s meetings with Moon. In November, Moon reportedly convinced Trump to visit the U.S. Army’s newly expanded Camp Humphreys to showcase that South Korea paid for 92 percent of the $10.7 billion project.

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Meanwhile, the U.S.-South Korea alliance has been tested amid a broader thawing in tensions between Seoul and Pyongyang, spurred in part by the Winter Olympics.

On Monday, top aides of Moon met with North Korean leader Kim Jong Un in Pyongyang in hopes of improving inter-Korea relations and helping start a dialogue between the United States and North Korea. The South Korean delegation’s trip to the North followed Pyongyang’s delegation to the Winter Olympics, held in Pyeongchang, South Korea.

Over the weekend, Trump said he “won’t rule out direct talks” with Kim, but said that North Korea has to “de-nuke.”

“And they, by the way, called up a couple of days ago and said, 'We would like to talk,’” Trump said at the Gridiron dinner. “And I said, 'So would we, but you have to de-nuke, you have to de-nuke.'”