But he confirmed reports that the US held "side negotiations" on the proliferation issue with North Korea last week in the hope of breaking the impasse.
Christopher Hill, the chief US nuclear negotiator, met his North Korean counterpart Kim Kye-gwan in Singapore to debate the form of the declaration last week.
Wilder said a US team of experts will be sent to Pyongyang next week on how to verify the accounting of its nuclear programmes and "to see if we can make progress" on the declaration.
Reports say the deal includes North Korea's demand to be removed from a US terrorism blacklist, as well as energy aid and major diplomatic and security benefits.
The disclosure issue has hindered progress in disarmament talks between North Korea and the US, China, Japan, South Korea and Russia.
"The US reserves the right to take whatever steps it needs to"
Condoleezza Rice, US secretary of state
The US has for months demanded that the North deliver a "complete and correct" list of all its nuclear activities including any proliferation of nuclear know-how, which it failed to do by the end of last year.
On Thursday, Condoleezza Rice, the US secretary of state, saying it will take time to verify the nuclear programmes or proliferation activities, hinted that US sanctions against the North could be removed earlier.
"Verification takes some time because these are complex programmes, this is a non-transparent society, there is a history here of surprises and so it will take some time – even past the second phase – for verification to completely play out," she said.
"Whatever is done in phase two, if it's demonstrated in phase three that somehow something was wrong in phase two, of course, the United States reserves the right to take whatever steps it needs to."
Rice said the document incorporating North Korea's proliferation activities could be kept private, allowing Pyongyang to save face.
"Not everything in diplomacy is public," she said, but added that the US congress would be briefed on any final arrangement.
"I want to emphasise that we are at the beginning of a very complex process, not the end, a process that must lead to the actual removal, for the first time in history, of nuclear material from North Korea and verifiable end to its nuclear programmes," Rice said.
The declaration had been held up partly because of Pyongyang's reluctance to discuss any transfer of nuclear technology to other countries, particularly Syria, as well as to account for its suspected pursuit of uranium enrichment.