(Newsweek) -- The earlier-than-expected move prompted protests by hundreds of local residents and was denounced by the frontrunner in South Korea's presidential election on May 9.

A spokesman for Moon Jae-in said the decision "ignored public opinion and due process" and demanded the deployment be suspended until the next administration was in place and had made its policy decision.

The United States and South Korea last year agreed to deploy the Terminal High Altitude Area Defense (THAAD) system to counter the threat of missile launches by North Korea. However the move has angered China, which says the advanced system will do little to deter the North while destabilizing the regional security balance.

South Korea's defense ministry said some elements of THAAD were moved to the site on what had been a golf course in the south of the country.

"South Korea and the United States have been working to secure an early operational capability of the THAAD system in response to North Korea's advancing nuclear and missile threat," the ministry said in a statement. The battery is expected to be operational by the end of the year, it added.

Television footage showed military trailers carrying large units including what appeared to be launch canisters being driven into the planned THAAD battery site, about 250 km (155 miles) south of Seoul. Images showed local protesters hurling water bottles at the vehicles and police trying to block them.

The Pentagon said the deployment was a critical measure to defend South Korea and its allies against North Korean missile threats and it would complete it "as soon as feasible".

The U.S. and South Korean militaries have been reluctant to publicly discuss the progress of the deployment ahead of the South Korean presidential election.

Moon, the favorite to win the race, has said the new South Korean administration should decide on whether to deploy the THAAD after gathering public opinions and having further discussions with Washington.

More than 10 protesters were injured during clashes with police and some of them had bone fractures, Kim Jong-kyung, co-head of a group of villagers protesting the THAAD deployment, told Reuters. Kim said about 200 protesters, mostly residents in two towns near the battery site, rallied overnight and would remain near the location.