SEOUL, South Korea — South Korea said Wednesday it will set up an environmental review before allowing four more launchers to be added to a contentious U.S. missile defense system meant to cope with North Korean threats.

The Terminal High Altitude Area Defense system has already been operational in southeastern South Korea with two launchers and a powerful radar. THAAD normally consists of six launchers, and the rest of four launchers have arrived in South Korea but haven't been deployed.

After taking office on May 10, South Korea's new liberal president, Moon Jae-in, said his office wasn't briefed by defense officials about the arrival of the four additional launchers and ordered an investigation. His office said Monday that a senior defense official was suspended for his failure to report the arrival.

Moon has also demanded an environmental assessment on the deployment site, saying there are suspicions that the Defense Ministry might be trying to avoid a thorough environmental inspection there.

Moon's moves caused media speculation about their motives. He had said during his election campaign that he would review a system that has enraged not only North Korea but also China, South Korea's largest trading partner.

On Wednesday, a senior presidential official told South Korean reporters the issues of the four launchers' deployment would be determined after the environmental assessment , according to Moon's presidential Blue House.

Analysts say the environmental test would make it difficult for the four launchers to be deployed this year. South Korean and U.S. officials had earlier said they aimed to deploy the system this year.

Seoul-based analyst Jung Chang Wook said that THAAD's six launchers are operated on a rotational basis so the delay of the four launchers would lead to the already-deployed two launchers being overused. He said, however, that there won't be any serious troubles in terms of THAAD operations.

It's unclear if Moon will go ahead with his campaign pledge to re-examine the THAAD deployment because a request for the withdrawal of the system's components could severely undermine ties with Washington, Seoul's most important ally, analysts say. The United States stations about 28,500 troops in South Korea as deterrence against potential aggression from North Korea.