The US is increasing pressure on South Korea to cooperate to enhance its advanced missile defense system, which it deployed here in 2018 to cope with rising military threats from North Korea.

The move might further complicate efforts by President Moon Jae-in’s government to gain Washington’s support for inter-Korean projects.

The US remains opposed to Moon’s recent suggestion that Seoul consider allowing South Korean citizens to make individual trips to the North. Officials in the Moon administration have said individual trips would not violate the US-led international sanctions imposed on Pyongyang in response to its nuclear and ballistic missile tests.

Concern about objections from China might also keep the Moon administration from working with the US to beef up the missile defense system, known as Terminal High Altitude Area Defense. South Korea suffered heavy economic losses after Beijing retaliated against a decision by the government of Moon’s predecessor, Park Geun-hye, to host the US anti-missile system, which China regards as a threat to its own security interests.

Washington’s latest move with regard to the anti-missile system can be understood as mainly an attempt to better cope with North Korea’s enhanced missile capabilities.

At a press briefing on Monday last week, US missile agency director Vice Adm. Jon Hill said separating the launchers from the rest of the system could allow for “a lot of flexibility on the peninsula.”

“You can put the launchers forward, you can bring in additional launchers,” he said.

The North fired 25 projectiles, including short-range ballistic missiles and a submarine-launched ballistic missile, in 13 rounds of tests last year. It now appears to be preparing to test-fire an intercontinental ballistic missile capable of hitting the US mainland, ending a hiatus on such tests since November 2017.

Seoul’s Defense Ministry said last week that it had been briefed by the US on its work to improve THAAD capabilities but no discussion had taken place on the possibility of relocating the launchers to other parts of the country from their current position in the central county of Seongju.

It also dismissed speculation that the US was to deploy more launchers on South Korean soil.

The ministry said in a press release that any additional measure regarding the THAAD system “is subject to prior discussions between South Korea and the US.”

Washington also seems to be using the anti-missile system issue to push Seoul to pay more for the US military presence here.

The 2021 budget proposal from the US Department of the Army, dated Feb. 3, said the possibility of South Korea funding the construction of the THAAD base on its soil “has been addressed.”

The proposal comes amid stalled negotiations between the allies on the Special Measures Agreement, which stipulates Seoul’s share of the costs of stationing US troops here.

There have been suspicions that the US might be seeking to include the base construction costs in the deal and to have South Korea pay. Under a 2017 accord between the allies on THAAD deployment, Washington is supposed to cover the construction costs while Seoul is to provide the site.

South Korea has yet to conduct a full-scale environmental survey of the Seongju site, where a six-launcher THAAD battery is installed on a temporary basis.

The allies should not let the anti-missile system issue further strain their defense ties.

The Moon government needs to recognize that its desire to improve inter-Korean relations cannot come before the need to defend against Pyongyang’s enhanced nuclear and missile capabilities. If necessary, more THAAD launchers should be deployed here, beyond upgrades to the existing system.

Seoul also has to complete the environmental survey at an early date to mitigate Washington’s displeasure over the delay in base construction.

The Moon government made a promise to China in 2017 not to expand the THAAD system. It was an inappropriate promise that critics say limits South Korea’s military sovereignty.

Nevertheless, installing more launchers could not be seen as violating the promise, as what Beijing took issue with was the far-reaching radar of the system, which it suspects could be used to spy on mainland China.

For its part, Washington needs to refrain from linking the anti-missile system to its demand for a steep increase in Seoul’s share of the cost for the upkeep of US forces in South Korea.