The US may move some of its anti-missile system - and it's sparking unease in South Korea

The US is relocating parts of a missile defence system installed in South Korea to the Middle East, according to officials cited by the Washington Post and South Korean news outlets.

The reported move comes 12 days into the US-Israeli war against Iran, and follows reports suggesting Iran had destroyed a key radar used by the Terminal High-Altitude Area Defense, or Thaad, system in Jordan.

Thaad was first deployed to South Korea in 2017 to protect against threats from nuclear-armed North Korea.

The move was met with anger and protests from South Koreans who feared it made them a bigger target, while China warned it could destabilise the region.

What is Thaad - and why might it be moved?

Earlier this week, the Washington Post reported that parts of the Thaad system were being moved to the Middle East, citing two officials.

The reports come as the US and Israel continue to strike Iran, and Iran responds with a barrage of drones and ballistic missiles targeting Israeli and US military bases in the region.

It's not clear exactly how many missiles Iran has - it has launched more than 500 ballistic missiles so far, according to a New York Times tally.

Most of them have been intercepted but the volume of incoming fire could be straining Washington's military inventory, observers say. And it's likely to continue because Iran, they believe, is readying itself for a war of attrition that ensnares more of the Middle East, including US allies.

That would explain why Thaad - which is specifically designed to intercept high-altitude missiles - is crucial for bolstering the US' defence system.

Reports earlier this month claimed that an Iranian strike destroyed the $300m radar of an existing Thaad system in Jordan.

Made by US company Lockheed Martin, the anti-missile system includes six mounted launchers, with eight interceptors on each launcher, and a radar system for detection.

It can shoot down short and medium-range ballistic missiles, using hit-to-kill technology. That is, kinetic energy destroys the incoming warhead. It can do this at a high altitude, beyond even the Earth's atmosphere, which was seen as especially useful in South Korea, because it could be used to intercept and destroy a nuclear warhead.

A single system, or battery as it's known, costs roughly $1bn (£766m) and requires a crew of about 100 personnel to operate. The US operates just eight of them globally, two of which are in the Middle East - Jordan and Israel. The UAE and Saudi Arabia together own three more in the region.

The potential redeployment from South Korea is a "precautionary measure", a US official told the Washington Post, but other analysts see a system stretched thin.

The move would strongly suggest "the need for the US to compensate for its heavy use of existing missile defence capabilities in the Middle East", Professor John Nilsson-Wright of Cambridge University told the BBC.

South Korean media outlets, including SBS and Yonhap, report that Thaad launchers are already being transported out of the Seongju airbase, south of Seoul.

President Lee Jae-myung acknowledged that Seoul had "expressed opposition" to the withdrawal of US weapons.

"It appears that there is controversy recently ⁠over US forces in Korea shipping some weapons, such as artillery batteries and air defence weapons, out of the country," he said in a cabinet meeting.

"While we have expressed opposition, the reality is that we cannot fully push through our position."

When asked if this would hinder Seoul's deterrence strategy, he responded: "I can say with certainty that it would not."

Lee's words were an "unusual public expression of opposition to the move, highlighting Seoul's legitimate concerns that this [could] compromise South Korea's defence capabilities", Nilsson-Wright said.

How have other countries reacted?

On Wednesday, when asked if Beijing had any comment on the possible relocation, China's Foreign Ministry Spokesman Guo Jiakun reiterated that "China's opposition to the US deployment of Thaad missiles in the Republic of Korea (ROK) remains unchanged".

China had been the most vocal critic when Thaad was installed in 2017.

For one, it boosted American military presence in the region, and provided a check on Beijing's growing power.

Washington and Seoul said the missiles were meant to stop attacks from the North, but China argued they had incredibly powerful radar allowing them to see deep into Chinese territory. So they could be used to spot Chinese missile launches, which affected Beijing's deterrent capability.

China retaliated by unofficially boycotting Korean goods, banning group tours to South Korea for six years, and even cancelling K-pop concerts.

While Beijing could celebrate the Thaad system being moved, it is unlikely to see that as a victory unless it becomes a "permanent removal", said Professor Ian Chong of the National University of Singapore.

However, Beijing could view the war in the Middle East as one that "distracts the US from its readiness in the Indo-Pacific", Nilsson-Wright said.

North Korea has yet to publicly comment. Nilsson-Wright said leader Kim Jong Un is unlikely to "exploit these changes" but other observers believe there is still some risk that he could test the South with small provocations.

And that raises the biggest question of all, Chong says: "Whether a prolonged conflict with Iran will deplete US missiles to a degree to which responding to contingencies elsewhere becomes difficult."