The United States and South Korea are moving forward in negotiations on the potential deployment of the THAAD missile defense system in the South, and are now focused on working out unspecified "complicated issues," the Pentagon said Monday.

Following the North's long-range missile test in February, Seoul and Washington launched official talks about placing a Terminal High Altitude Area Defense battery in the South to bolster defense against missile threats from the communist nation.

The move has irked China, which claims the powerful THAAD radar can be used to spy on it.

The issue has drawn renewed attention after a senior U.S. official was quoted as saying last week that there will be a "public announcement soon." The remark was seen as meaning that the two sides are close to agreement on THAAD deployment.

"Those alliance negotiations continue and my understanding is they are proceeding as planned and we are working through the complicated issues that need to be worked out before that deployment can move forward," Pentagon press secretary Peter Cook said at a press briefing.

Cook said, however, that the issue did not come up when Defense Secretary Ash Carter held talks with South Korean Defense Minister Han Min-koo in Singapore on the sidelines of the annual regional defense ministers' meeting called the Shangri-La Dialogue.

"There were extensive discussions with the South Koreans over a range of issues. That specific issue did not come up," Cook said.

"So a range of topics with regard to the U.S.-South Korea alliance and strong defense relationship. But specifically, the topic of THAAD negotiations did not come up."

In Seoul, government sources said that the THAAD talks have moved forward to a point where the two sides are now looking into multiple candidate sites for deployment, including not only existing U.S. military bases, but also mountainous areas away from cities.

Speculation has it that the two sides could announce deployment during October's defense ministers' talks.

Meanwhile, Defense Minister Han said in an interview with CNN that THAAD's deployment will "dramatically" enhance Seoul's capacity to counter North Korea's missile threats.

"South Korea only has the capacity to intercept missiles at its terminal phase. So we have limitations. If THAAD is deployed to U.S. forces in Korea, our capability will be dramatically enhanced.

There are definite military benefits to this," Han said in the interview broadcast Monday morning. (Yonhap)