Senior U.S. officials raised pressures on South Korea "indirectly" to deploy its advanced missile defense system, called Terminal High Altitude Area Defense (THAAD), on the Korean Peninsula, causing an unpleasant reaction from some South Koran officials.

U.S. Secretary of State John Kerry touched off controversy, saying during his two-day visit to Seoul that "provocative activities" and nuclear ambitions by the Democratic People's Republic of Korea (DPRK) led the United States to be "talking about THAAD."

It was Kerry's first mentioning, since he took office in February 2013, of the THAAD deployment on the peninsula, though in an indirect manner. The comments were made during his meeting with the service members of the U.S. Forces Korea (USFK) at Yongsan garrison in Seoul.

The pressures got stronger as another U.S. official indicated what Kerry meant. Frank Rose, assistant U.S. secretary of state for arms control, verification and compliance, was quoted by Yonhap News Agency as saying Tuesday that the U.S. "is considering the permanent stationing of a THAAD unit on the Korean Peninsula."

His comments were made in Washington at a seminar hosted by the Institute for Corean-American Studies (ICAS), after Kerry " unexpectedly" mentioned the THAAD deployment, of which he made no mention during a joint press conference with South Korean Foreign Minister Yun Byung-se.

A senior U.S. military official also mentioned the need for the missile defense system. Adm. James Winnefeld, vice chairman of the U.S. Joint Chiefs of Staff, said Tuesday that if the DPRK eventually develops a submarine-launched ballistic missile (SLBM) technology, it would place a hard-to-detect danger on South Korea, Japan and U.S. troops stationed in the region.

The admiral said the issue would be left to diplomats and negotiators, but he noted that "when it's ripe, I'm sure we'll get into that."

Both Rose and Winnefeld said that the U.S. had "no formal consultations" with South Korea on the deployment of the THAAD missile interceptor battery on the peninsula.

The indirect pressures from senior U.S. officials came as the DPRK said on May 9 that it had successfully test-fired a ballistic missile from a submarine, posing serious threats to South Korea and the U.S. mainland as the SLBM can mean the DPRK's submarine secretly sailing underwater and staging missile strikes against the U.S. soil.

The U.S. plot to deploy the THAAD battery on the Korean Peninsula on the pretext of the DPRK threats caused an unpleasant reaction from some South Korean officials as such pressures were put though no formal consultations are launched.

An unidentified South Korean government official was quoted by Yonhap News Agency as saying that the remarks by Rose "seemed to go too far" as he is not in charge of the THAAD policy of the U.S. government.

Another official said that the government was at a stage of making a working-level review on whether the THAAD deployment would be needed from the perspective of defense capability and efficiency, adding that he would not respond, in detail, to comments by U.S. officials.

South Korea's presidential spokesman Min Kyung-wook told reporters Wednesday that the U.S. purportedly had yet to complete internal discussions, noting that Washington had yet to make a formal request for Seoul over the THAAD issue.

Min said that if the U.S. formally requests, South Korea would make a decision on its own after comprehensively considering the military effectiveness and the national interests of security.

His comments represent South Korea's "strategic ambiguity" position on the THAAD deployment, also called three "No"s -- No request from the U.S., No consultation on the issue, so No decision on the deployment.