The meetings follow North Korea's failure to deliver a full declaration of all its nuclear programmes by the end of 2007.
The deadline was a key part of a six-nation aid for disarmament deal agreed in Beijing in February between diplomats from North and South Korea, Japan, China, Russia and the US.
North Korea said on Friday that it had already accounted for its nuclear arms programme as required under the deal, but the assertion was quickly rejected by the United States.
"They were prepared to give a declaration which wasn't going to be complete and correct and we felt that it was better for them to give us a complete one even if it's going to be a late one," Hill told reporters in Tokyo.
"We understand that this is always a difficult process, one that is never, rarely completed on time. So I think we have to have a little sense of patience and perseverance."
In its statement last week, North Korea's foreign ministry accused the US and other participants in the six-nation talks of not carrying out their commitments.
It cited delays in shipping energy aid and removing the North from US terrorism and trade blacklists.