The United States began installing a contentious missile system in South Korea on Wednesday, as tensions continue to mount over Pyongyang’s growing nuclear ambitions.

The partial deployment of the THAAD anti-missile defence system has sparked protests from local residents and condemnation from the frontrunner in South Korea's upcoming presidential election.

Defence officials in Seoul confirmed that some elements of the system were installed on Wednesday and that it will be operational by the end of the year, several reports said.

The move was “in response to North Korea's advancing nuclear and missile threat" a statement said, amid concerns that Pyongyang was planning a nuclear test, its sixth since 2006.