SEOUL — The United States and South Korea have failed to agree on a bigger South Korean share of the cost of maintaining U.S. troops, an official said on Friday, as the U.S. military warned Korean workers they might be put on leave if no deal is reached.

President Donald Trump has repeatedly said that South Korea should bear more of the burden for keeping some 28,500 U.S. troops in South Korea, where the United States has stationed forces since the 1950-53 Korean War.

Senior officials from both sides held three-day talks in Seoul from Tuesday to hammer out an accord to replace a 2014 deal due to expire this year, which requires South Korea to pay about $850 million this year.

Despite 10 rounds of negotiations since March, the two sides struggled to reach an agreement after the United States demanded a sharp increase, South Korean officials said.

"We've come to agreement on almost all elements but could not make it final because of differences on the total scale of the deal," a senior South Korean foreign ministry official told reporters on condition of anonymity due to the sensitivity of the issue.

The United States initially pushed South Korea to increase its share of the burden to about $1.2 billion, The Wall Street Journal reported last week, citing unidentified sources.

South Korean officials have not publicly confirmed a dollar amount, and U.S. Forces Korea did not have immediate comment.

South Korean officials have said the United States asked that South Korea pay for the mobilization of equipment, such as bombers, nuclear-powered aircraft carriers and submarines, during joint military exercises.

Trump announced a halt to the exercises in June after a summit with North Korean leader Kim Jong Un, saying they were very expensive and paid for mostly by his country.

Some small-scale joint exercises have taken place since then, while major ones were suspended as part of efforts to expedite talks aimed at ending North Korea's nuclear program.

The South Korean official said the two sides were not expected to meet again this year, raising the risk of a funding gap.

Last month, U.S. Forces Korea warned South Korean workers some of them might have to "furlough," or go on leave, from mid-April if a deal could not be reached.

About 70 percent of South Korea's contribution covers the salaries of some 8,700 employees who provide administrative, technical and other services for the U.S. military.

"We are making efforts to minimize any negative impact that may have on the employees," said the ministry official.