The US has deployed an additional Patriot missile battery in South Korea, the military said on Saturday, ahead of talks to set up an even more sophisticated US defence system - a move that has worried China and Russia.
The US military command in South Korea said an air defence battery unit has been conducting ballistic missile training using the Patriot system at Osan Air Base near Seoul.
Lt Gen Thomas Vandal said "exercises like this ensure we are always ready to defend against an attack from North Korea".
"North Korea's continued development of ballistic missiles against the expressed will of the international community requires the alliance to maintain effective and ready ballistic missile defenses," Vandal said in a statement.
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The new tough stance follows South Korea's decision to shut down an inter-Korean factory complex that had been the rival Koreas' last major symbol of cooperation, but that Seoul said had been used by North Korea to fund its nuclear and missile programmes.
North Korea responded by deporting South Korean citizens, seizing South Korean assets and vowing to militarise the park.
South Korea on Friday cut off power and water supplies to the industrial park and announced that its planned talks with the US on deploying the Terminal High-Altitude Area Defense, or THAAD, one of the most advanced missile defense systems in the world, could start next week.
South Korean media have long speculated that the two countries are working on a THAAD deployment in South Korea, but it took the North's rocket launch last Sunday, which outsiders see as a test of banned ballistic missile technology, for the allies to formally announce they will begin the missile defence talks.
Beijing and Moscow are sensitive to the possibility of THAAD in South Korea. Critics say the system could help US radar spot missiles in other countries.
China's state media quickly made the country's displeasure known, while Russia also expressed worries about the deployment.
North Korea has previously warned of a nuclear war in the region and threatened to bolster its armed forces if the THAAD deployment occurs.
READ MORE: South Korea cuts off power to complex in the North
In Munich, US Secretary of State John Kerry met with his Chinese and South Korean counterparts to discuss the response to North Korea's actions, including the missile system.
"That's what we're talking about today," Kerry told reporters Friday on the sidelines of a Munich security conference.
Seoul and Washington want to deploy the system at an early date and the upcoming talks will discuss where and exactly when the deployment can be made, a South Korean defence official said, requesting anonymity because of department rules.
The official said the THAAD deployment is designed to protect South Korea from North Korean threats and isn't targeting China or anyone else.
The current standoff flared after North Korea carried out a nuclear test last month, its fourth, followed by the long-range rocket launch on Sunday.
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