U.S. Defense Secretary Mark Esper on Friday pressed Washington’s case that longtime ally South Korea must pay a bigger share of the cost of having U.S. troops on its soil, Eurasia Diary reports citing Associated Press.

“This is a very strong alliance we have, but Korea is a wealthy country and could and should pay more to help offset the cost of defense,” Esper told a joint news conference with his South Korean counterpart, Jeong Kyeong-doo.

Esper said that while South Korea has provided “a fair amount of support in the past,” it is important to point out that “most of that money stays here in this country -- easily over 90% of that money stays here in Korea, it does not go to the United States.”

The amount Korea pays for the presence of about 28,000 U.S. troops has varied over the years. This year it is nearly $1 billion.

South Korean news reports have said the Trump administration is demanding a five-fold increase in South Korean contributions, to about $4.7 billion for 2020, although Jeong declined to confirm the figure. He said his country was prepared to pay a “fair and reasonable” amount.

In remarks to reporters Wednesday as he was flying to Seoul, Esper declined to cite a figure but said the administration has asked for a “substantial increase” in South Korea’s contributions.

At Friday’s news conference, Esper said American demands for a more favorable sharing of defense costs applies not only to South Korea but also to allies and partners across the globe. President Donald Trump has long accused American allies in Europe and Asia of being freeloaders and questioned why the U.S. is still helping to defend them.

Negotiations with Seoul over cost-sharing for 2020 is one of several major irritants in the alliance, which dates to the 1950-53 Korean War when the U.S. and other nations intervened after North Korea invaded the South.