South Korea said Monday that it still plans to host an advanced American anti-missile battery, and to get it operating as soon as possible, as Vice President Mike Pence arrived in the country for meetings with political leaders.

Plans to deploy the Terminal High Altitude Area Defense (THAAD) system have been controversial in South Korea, with some worried that it would make the South more of a target for North Korean missiles, and others concerned about the economic revenge being exacted by China.

The issue is expected to be near the top of the agenda Monday when Pence meets with Hwang Kyo-ahn, South Korea's acting president, and the speaker of the parliament.

Hwang has less than a month left before a snap presidential election will be held May 9 to replace Park Geun-hye, who was impeached last month, and the front-runner has vowed to review the THAAD decision.

"There is no change in the basic position of South Korea and the U.S.toproceed, as planned, with the preparations for the early operation of the THAAD system against North Korea's advancing nuclear and missile threats," Moon Sang-gyun, a spokesman for the Ministry of National Defense, said at a news briefing Monday morning, according to local reports.

Park's conservative governmentagreed to deploy THAAD, after much equivocation, in July. China strongly objects to the THAAD battery - in particular its radar system, which Beijing worries will be used to peer into China.

Beijing has made its unhappiness known with awideeconomic boycott that includes K-pop concerts, toilet-seat imports and tour group travel to South Korea.

But Moon Jae-in, a progressive presidential candidate who had been leading in polls, has promised to review the previous government's decision to host THAAD. Apparently sensing a worsening political environment, the U.S.militarysped up the deployment to try to get everything in place before the election.

But now Moon faces a strong challenge from a more centrist candidate, Ahn Cheol-soo, who has said that he will respect the Park administration's agreement with the United States.

Pence expects the issue to come up during this trip.

"It's a critical point for the defense of South Korea in recognizing it's not an offensive weapon. It's there to prevent rockets slamming from the North Koreans," a White House official said while previewing the trip.

The complicating factor here is China. It wants the missile battery gone, and the United States wants China to crack down on North Korea.

Although President Donald Trump had a cordial summit with his Chinese counterpart, Xi Jinping, in Florida this month, the North Korea issue threatens to drive a wedge between them.