The United States says that the planned deployment of its Terminal High-Altitude Area Defense (THAAD) system in South Korea is not negotiable.
The THAAD system will be installed by the end of next year to defend South Korea against nuclear and missile threats from North Korea as Seoul and Washington claim.
Daniel Russel, a senior US diplomat for Asia, said on Friday that Washington and Seoul have agreed upon the installation of the system and cannot negotiate their deal.
"No. The two countries have made a decision,” Russel, the US assistant secretary of state for East Asia, told reporters when asked whether THAAD was negotiable.
China, a North Korea's main ally, is strongly opposed to the plan, but has expressed its anger over North Korea’s repeated missile and nuclear tests in the region.
Pyongyang says the tests aim to protect itself from the US military, which occasionally deploys nuclear-powered warships and aircraft capable of carrying atomic weapons in the region.
North Korean Foreign Minister Ri Yong-ho said Friday that the sole way to defend itself against the US is “going nuclear.”
The comments came two weeks after the country conducted its fifth nuclear blast in the face of crippling sanctions.
The UN and the West have so far imposed a raft of sanctions on North Korea, prompting Pyongyang to step up its nuclear activities.
Russel said that a new UN resolution on North Korea would be agreed soon, imposing further sanctions and tightening existing ones against the country.
He said the sanctions would prevent Pyongyang from abusing international infrastructure, including banking and shipping, and furthering its nuclear program.
"The international system is being exploited by (North Korea) ... for the purpose of pursuing an illegal nuclear and missiles program that threatens both its neighbors and regional peace and security," Russel stated.