President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE's national security adviser on Sunday told his South Korean counterpart that the U.S. would shoulder the cost of the THAAD missile defense system, Reuters reported.

In a phone call to South Korea's national security chief, Kim Kwan Jin, national security adviser H.R. McMaster said the U.S. would honor a 2016 pact between the two countries requiring the U.S. to bear the cost of the system, intended to protect against a North Korean missile attack.

The call apparently walked back comments made by Trump earlier this week in an interview with Reuters, in which he said he thought South Korea should pay for the system.

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"I informed South Korea it would be appropriate if they paid. It's a billion-dollar system," he said. "It's phenomenal, shoots missiles right out of the sky."

But South Korea's Defense Ministry promptly rejected that notion, citing the 2016 agreement.

"There is no change in South Korea and the United States’ position that our government provides the land and supporting facilities and the U.S. bears the cost of THAAD system’s deployment, operation and maintenance," South Korea's Defense Ministry said in a statement.

The U.S. began moving parts of the missile defense system to a South Korean deployment site earlier this week amid increasing tensions with North Korea.