A senior U.S. diplomat on Monday said Washington was prepared to "keep the screws to North Korea" until it ceases its nuclear-weapons work, Agence France-Presse reported.
"Pyongyang’s attempts to engage in dialogue while keeping its program running are completely unacceptable," U.S. special envoy for North Korea policy Glyn Davies said to journalists in Tokyo.
Davies was wrapping up a tour of East Asia where he held talks with Chinese, South Korean and Japanese officials on the long-running impasse over North Korea's nuclear program.
"If [the North Koreans] do not act to demonstrate that they understand they must fulfill their obligations and give up their nuclear weapons, then there is more pressure that will be brought to bear on them," the diplomat said.
North Korea has been under heightened U.S. and international sanctions for years but they do not appear to have kept it from advancing its nuclear weapons work in several key areas. Those include the development of long-range ballistic missile capabilities, more powerful nuclear devices and uranium-enrichment centrifuges that can be built indigenously.
Davies suggested new economic penalties could be in the offing: "We believe sanctions and pressure are key in sharpening choices that Pyongyang faces."
Washington, Seoul and Tokyo are demanding that Pyongyang cease efforts to produce plutonium and enriched uranium as a precondition to the resumption of the frozen six-nation nuclear talks.
The North Korean Foreign Ministry on Tuesday responded to Davies' comments by accusing Washington of making "absurd" demands and trying to sabotage the six-party talks process, the Yonhap News Agency reported.
"[We] will never accede to unreasonable preconditions raised by the U.S.," an unidentified ministry spokesman was quoted by regime media as saying. "[North Korea] remains unchanged in its goal for the denuclearization of the whole of the Korean Peninsula, but it will be compelled to steadily bolster deterrence as long as the U.S. becomes all the more undisguised in pursuing hostile moves."