It follows North Korean dictator Kim Jong Un's pronouncement that the country's nuclear warheads should be "ready for use at any time
"Under the extreme situation that the U.S. Imperialist is misusing its military influence and is pressuring other countries and people to start war and catastrophe, the only way for our people to protect sovereignty and rights to live is to strengthen the quality and quantity of nuclear power and realize the balance of power," Kim said, according to state news agency KCNA.
The news agency also confirmed the test-fire of a new multiple launch rocket system the previous day.
In response, the South Korean Defense Ministry said it would begin "negotiation regarding deployment" of THAAD.
Officials will "discuss the possibility of the deployment of THAAD which will be operated by US Forces in Korea in South Korea in one of the series of efforts to develop missile defense system of the South Korea -- U.S. alliance."
Initial discussion to deploy THAAD started following a purported North Korean hydrogen bomb test. The system is not without controversy however, and on Friday Chinese Foreign Ministry spokesman Hong Lei reiterated Beijing's opposition to the deployment of THAAD in South Korea, adding that China hoped relevant countries would "act cautiously and not damage China's strategic security interests."
What is THAAD?
Made by the U.S. Army, THAAD is designed
to shoot down short, medium and intermediate ballistic missiles, just the type of weapons North Korea claims it has.
Because it has no warheads on its missiles, instead destroying other projectiles by colliding with them, THAAD is "potentially safer, especially for dealing with nuclear missiles," said Yvonne Chiu, an expert on military policy and diplomacy at Hong Kong University.
"If you hit a nuclear ballistic missile with a missile with no warhead, it would hopefully not cause a nuclear explosion."
Unlike North Korea's mostly untested ballistic missiles program, THAAD has been in use for several years by the U.S. military to protect units in places such as Guam and Hawaii from potential attack.
"North Korea continues to develop their nuclear weapons and ballistic missile programs, and it is the responsibility of our Alliance to maintain a strong defense against those threats," Gen. Curtis M. Scaparrotti, Combined Forces Command, U.S. Forces Korea commander said last month.
"THAAD can add an important capability in a layered and effective missile defense."
Why is it controversial?
While the U.S. maintains that any deployment of THAAD in South Korea would be solely to protect its forces there and their South Korean allies, some see it as further militarization of the peninsula and an escalation of the American presence there.
China especially, tends to view any increase in U.S. military presence in Asia as an attempt to contain it and reduce the effectiveness of its weapons.
Speaking at an event hosted by the Center for International and Strategic Studies think tank in February, Chinese Foreign Minister Wang Yi said the deployment of the anti-missile system could jeopardize "China's legitimate national security interests."
"THAAD has a range that could hit weapons in China," said HKU's Chiu.
While she added that the significance of THAAD deployment in Korea would be more geopolitical than military, Chiu said that China was understandably concerned "about having a U.S. made, U.S. run missile system in its backyard."
"Whenever you add something new, it automatically causes concerns."
"THAAD Is a purely defensive weapon, it is purely capable of shooting down a ballistic missile it intercepts and it is there for the protection of the United States," Secretary of State John Kerry said last month during a visit to Beijing
"Russia and China have obviously expressed concerns about THAAD," he said.
"We have made it very clear we are not hungry or anxious or looking for an opportunity to deploy THAAD.
If we can get to denuclearization, there's no need to deploy THAAD."