The United States and South Korea are in formal discussions about the THAAD missile defense system with the aim of deploying the system at the "earliest possible date," a senior State Department official said.

Frank Rose, assistant secretary of state for arms control, made the remark during a missile defense conference in London, saying THAAD will provide "an essential defensive capability" against North Korea's extended-range Scud and Rodong missiles.

"We also work closely with the Republic of Korea on missile defense issues. In response to the evolving threat from North Korea, including its nuclear weapon and ballistic missile programs, we made an alliance decision in February to begin formal consultations on the viability of basing a THAAD system in the ROK," Rose said.

"The goal of the formal consultations is to bilaterally pursue the feasibility of deploying THAAD to and operating on the Korean Peninsula at the earliest possible date," he said, according to a transcript provided by the department.

Shortly after the North's long-range rocket launch in February, South Korea and the U.S. jointly announced they would begin official discussions on the possible placement of the U.S. Terminal High Altitude Area Defense (THAAD) missile defense system in the South.

That ended more than a year of soul-searching by Seoul over how to deal with the issue amid Washington's desire to deploy the system and China's intense opposition to it. The North's twin provocations of its fourth nuclear test on Jan. 6 and then a missile test a month later gave Seoul justification for the decision.

China has claimed THAAD can be used against it, despite repeated assurances from Washington that the system is aimed only at deterring North Korean threats. (Yonhap)