"While we will not comment about intelligence reports, we have come to expect North Korea to act recklessly and dangerously," said National Security Council spokesman Mike Hammer in a statement.

"But while the world unites to pass a strong new Security Council resolution, it is clear that North Korea's behavior is succeeding only in further isolating itself," Hammer added.

The North last month tested its second nuclear bomb, heightening a showdown after its testing in April of a long-range missile and withdrawing from a US-backed six-nation denuclearization deal.

US intelligence officials have warned President Barack Obama that North Korea intends to respond to a UN resolution condemning its actions with another nuclear test, Fox News reported, citing US intelligence sources.

The Central Intelligence Agency also uncovered, Fox said, that the North plans to reprocess its plutonium fuel rods into weapons-grade plutonium, boost its uranium enrichment program and launch another Taepodong-2 intercontinental ballistic missile.

Also citing unnamed US officials, CNN television said there are "fresh indications" North Korea could be preparing another nuclear test.

The move comes as US special envoy on North Korea Stephen Bosworth said the United States was committed to diplomacy even as the UN Security Council moved to expand sanctions.

"The United States and our allies and partners in the region will need to take the necessary steps to assure our security in the face of this growing threat," Bosworth told the Senate Foreign Relations Committee on Thursday.

He added, however, that in "the interest of all concerned, we very much hope that North Korea will choose the path of diplomacy rather than confrontation,", referencing US hope for a resumption of the six-party talks, which involved China, Japan, the two Koreas, Russia and the United States.