Yonhap said that the denial was issued during a news broadcast late on Thursday on North Korea's Central Television Station.
"Recently, the US ruling circle, which had been accusing us of being an 'outpost of tyranny' or a 'rogue state', finally came up with fabricated allegations that missile testing is imminent or there are signs of us preparing a nuclear test," the channel's news reader was quoted as saying.
Though North Korea's media is tightly controlled, experts in Seoul, the South's capital, said the comment by a news presenter for domestic consumption should be treated with caution and was unlikely to represent official policy.
Major North Korean policy announcements are normally issued by a Foreign Ministry spokesman through the official Korean Central News Agency.
This month, North Korea's Foreign Ministry issued a statement accusing Washington of raising fears about a nuclear test, but neither confirmed nor denied whether it was planning to carry out such a test.
North Korea has not confirmed
or denied the test
However, North Korean officials flatly denied the reports that the communist country was preparing to conduct a nuclear test to a group of Czech parliamentarians who were in Pyongyang this week.
"Officials of North Korea's Supreme People's Assembly dismissed the reports (of a nuclear test) as groundless propaganda," Lubomir Zaoralek, chairman of the lower house of the Czech Parliament, told reporters here on Wednesday on his return from a four-day stay in North Korea.
The six-member Czech delegation met with North Korean leaders, including Pyongyang's number two, Kim Yong-Nam, and SPA chairman Choe Tae-Bok.
The North Korean officials said rumours of a test were Washington's ploy to isolate the communist state.
Recent US media reports, quoting officials in Washington, said there were signs the North was preparing for a nuclear test.
North Korea declared itself nuclear-armed in February and said it had unloaded 8000 spent fuel rods from its nuclear reactor, a step that would allow it to reprocess weapons-grade plutonium for more nuclear bombs.