Arrival of THAAD angers North Korea as well as China and Russia which see its powerful radars as a security threat.
China is warning it will take measures against a US missile defence system deployed in South Korea, with the stated objective of countering threats from North Korea.
The equipment needed to set up Terminal High-Altitude Area Defence system (THAAD), a missile defence system, have arrived in South Korea, according to American and South Korean defence forces.
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The deployment announcement was made on Tuesday, a day after North Korea test-launched four ballistic missiles into the sea near Japan.
Admiral Harry Harris, head of the US Pacific Command, said in the statement that “continued provocative actions by North Korea, to include yesterday’s launch of multiple missiles, only confirm the prudence of our alliance decision last year to deploy THAAD to South Korea”.
The plans to deploy THAAD within this year have angered not only North Korea, but also China and Russia, which see the system’s powerful radars as a security threat.
China responded quickly, saying it would take “necessary measures” to protect itself and warning that the US and South Korea should be prepared to bear the consequences.
The US and South Korea say the system is defensive and not meant to be a threat to China or Russia.
THAAD can intercept and destroy short- and medium-range ballistic missiles during the last part of their flights, according to the US military.
On Monday, North Korea fired four ballistic missiles in an apparent protest against ongoing US-South Korean military drills that it views as an invasion rehearsal.
The missiles flew about 1,000km on average, three of them landing in waters that Japan claims as its exclusive economic zone, according to South Korean and Japanese officials.
On Tuesday Ju Yong-choi, a North Korean diplomat, told the UN-sponsored Conference on Disarmament in Geneva that the annual drills were “a major cause of escalation of tension that might turn into actual war” on the divided Korean peninsula.
“The ongoing joint military exercise is carried out with massive mobilisation of troops, unprecedented in size, and various types of US strategic forces including nuclear carriers, nuclear strategic bombers and Stealth fighters,” Ju told the 61-member forum.
“It will certainly jeopardise peace and stability in the region and drive the situation in the Korean peninsula to the brink of nuclear war.”