US President Donald Trump on Friday called for South Korea to pay $1 billion for a missile shield’s deployment here, and vowed to renegotiate a bilateral free trade pact, stirring heated reactions in South Korea.

Amid intense debate at home and diplomatic friction with China, key components of the Terminal High Altitude Area Defense system including a radar, launchers and interceptors were brought Wednesday to the planned deployment site in Seongju, North Gyeongsang Province. Seoul secured use of the land and the US Forces Korea is responsible for the installment and management of the system. 

“Why are we paying a billion dollars? So I informed South Korea it would be appropriate if they paid,” Trump said in an interview with Reuters, stressing the system is intended to protect South Korea.

“It’s phenomenal. It’s the most incredible equipment you’ve ever seen -- shoots missiles right out of the sky. … We’re going to protect them. But they should pay for that, and they understand that.”

Trump’s remarks stoked concerns he has set out to materialize his commitment to having allies and partners pay for what he has called a “fair share” of defense costs.

Seoul refuted his argument on THAAD, saying it has not been “informed” of any payment. The deployment plan had also been settled in line with the South Korea-US Status of Forces Agreement, which governs the stationing of some 28,500 US troops here, the foreign and defense ministries said.

“Our basic position remains unchanged that according to SOFA, we provide the land and related facilities and the US will pay for the THAAD system’s operation and maintenance costs,” the Defense Ministry said in a statement.

An official at the Foreign Ministry said the same, adding that it plans to lodge a complaint to Washington over what he called a “diplomatic discourtesy.”

On the free trade agreement between the two countries, Trump pledged to renegotiate or terminate the “horrible” deal, saying he would announce it “very soon.”

“It’s unacceptable,” Trump said, citing deepening trade deficits. “It’s a great deal for South Korea. It’s a terrible deal for us.”

According to the US Census Bureau, the country’s trade deficit in goods with South Korea grew from $16.6 billion in 2012 to $27.7 billion in 2016.

Data from the Korea International Trade Association put the increase at from $15.2 billion to $23.2 billion during the same period.

Seoul argues automobiles are a small fraction of two-way trade, and has been seeking to import more energy from the US while encouraging its companies to invest more there.

During a visit to Seoul last week, US Vice President Mike Pence also said his administration will “review and reform” the free trade agreement, saying it retains “too many barriers” for American companies.

On the campaign trail, Trump denounced the pact as a “job killer,’ especially for the US auto industry.

Trump also said there is a possibility of a “major conflict” with North Korea, though he pursues a diplomatic solution despite difficulties.

“There is a chance that we could end up having a major, major conflict with North Korea. Absolutely,” he said.

“We’d love to solve things diplomatically but it’s very difficult.”

With THAAD being a subject to fiery dispute ahead of the May 9 election, the interview drew stinging rebukes from some of South Korea’s leading presidential candidates.

Frontrunner Moon Jae-in’s Democratic Party of Korea and the progressive splinter Justice Party called for a halt in the ongoing installment process.

“It’s become obvious now that there was a grave flaw in the deployment decision in the first place,” Youn Kwan-suk, chief spokesperson for the Moon campaign, said at a press briefing.

“As the THAAD program would have a substantial impact on security and inflict massive economic costs, it’s essential to seek approval from the National Assembly. Moon has been consistent and clear that the issue should be reexamined by the next government.”

The Justice Party’s flag-bearer Sim Sang-jeung, who opposes the THAAD stationing, took issue with Wednesday’s surprise equipment transfer and demanded clarifications during a meeting with Marc Knapper, deputy chief of the US Embassy here.

“I’m so angry,” Sim said at a rally in Seoul, referring to Trump’s comments on THAAD and the FTA. “I will say to Trump here, you cannot force us to pay for THAAD after deploying it in a hit-and-run manner without the consent of our people. Or you could take it away again.”

The center-left People’s Party, whose candidate Ahn Cheol-soo backs the deployment, questioned whether Trump made his own argument or there has been a behind-the-scene compromise between Seoul and Washington.

“As agreed initially, the US should bear the entire deployment, operation and maintenance expenses,” party spokesperson Son Kum-ju said in a commentary. “Existing agreements must be fulfilled whether it be THAAD or the FTA.”

Despite its support for the plan, the minor conservative Bareun Party criticized Trump’s demand as “beyond the existing agreement and a matter of trust between the two countries,” calling for clarifications from Washington.

The far-right Liberty Korea Party argued Trump’s remarks reflected Washington’s concerns over a possible birth of a “leftist government” that pushes for a withdrawal of US forces here.

“Trump’s mentioning of the $1 billion payment is not unrelated to the domestic political situation,” spokesperson Kim Myung-yeon said at a briefing, adding that the party’s Hong Joon-pyo is the only contender who can challenge Trump.

By Shin Hyon-hee (heeshin@heraldcorp.com)