Glyn Davies, the US special representative for North Korea policy, said he hoped quickening diplomacy examining when to resume stalled six-party talks would bear fruit.
The talks are designed to push the reclusive state to abandon its nuclear ambitions, but have been in limbo since December 2008.
"Pyongyang's attempts to engage in dialogue while keeping its programme running are completely unacceptable," Davies told reporters after a meeting with his counterparts in Tokyo.
North Korea is currently pushing for a resumption of the six-party talks, but the United States says it must first demonstrate a commitment to denuclearisation.
US President Barack Obama's administration has repeatedly voiced frustration over its dealings with North Korea, but critics have said the issue has faded from US priorities.
Analysts have also expressed doubts over the effectiveness of the six-party framework, which critics say allows Pyongyang to make promises it feels free to renege on later.
Davies warned that it was difficult to draw direct comparison between North Korea and Iran, but highlighted the fact that the use of sanctions led to success with Tehran.
Davies said the United States was in close consultation with China to examine the right "threshold" to allow the resumption of six-party talks, which group the two Koreas, China, Japan, Russia and the United States.
"We believe sanctions and pressure are key in sharpening choices that Pyongyang faces," he said.
If North Korea fails to comply with the demands of the international community, "we will have to amp up that pressure in order to continue to try to bring home to them that this is a mistake," Davies said.
"There is still a room for diplomacy," he added.
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