Setbacks have plagued negotiations on the North's nuclear activities
North Korea has said it will not allow inspectors to take samples from its main nuclear complex to verify its account of past nuclear activities.
Pyongyang said it had never agreed to such a move, contradicting a statement by US officials last month.
Washington removed North Korea from its list of countries sponsoring terrorism saying the North had agreed to provide full access to its nuclear facilities.
The different interpretations may prove a new snag in disarmament negotiations.
North Korea's foreign ministry said last month's breakthrough agreement allowed for nuclear inspectors to visit its main Yongbyon complex, view documents and interview scientists - but that sample-taking was not part of the deal.
It is an act of infringing upon sovereignty little short of seeking a house-search... to insist on adding even a word except the written agreement
It also said Yongbyon would be open to inspection only after it received all the energy aid pledged by its negotiating partners - China, Japan, South Korea, the US and Russia.
"It is an act of infringing upon sovereignty little short of seeking a house-search... to insist on adding even a word except the written agreement," the North said in a statement.
The deal to remove North Korea from the US terror sponsors' list last month came after a visit to Pyongyang by US envoy Christopher Hill, and days of six-party talks.
US State Department officials said that in return the North had agreed to allow nuclear experts to take samples and conduct forensic tests at all its declared nuclear facilities and undeclared sites, on mutual consent.
It also said the North would allow inspectors to verify that it had told the truth about transfers of nuclear technology and an alleged uranium programme - which Pyongyang has always denied.
The US said North Korea would resume its disablement of nuclear facilities, in line with a nuclear disarmament-for-aid deal in 2007.
North Korea began disabling its Yongbyon nuclear reactor in August, but more recently it made moves to reassemble the plant after Washington refused to remove it from its blacklist.
In other provocative steps, it expelled UN inspectors and test-fired short-range missiles, heightening tensions with the US.