"We hope North Korea will submit a declaration as soon as possible so as not to lose good timing," Yu told reporters in Washington on Wednesday during a news conference with Condoleezza Rice, the US secretary of state.
Lee Myung-bak, South Korea's president who took office last month, favours a tougher stance to North Korea than his predecessors.
South Korea's unification ministry has declared that improvements in ties with Pyongyang will be determined by progress in the North's promise to abandon its nuclear weapons.
Lee has also said he will not shy away from pressing the North to improve its human rights record.
His posture represents a marked departure from the previous decade of rule by liberal presidents and their promotion of a so-called "sunshine policy" of reconciliation with the North.
Media reports earlier this week suggested Seoul would for the first time back a resolution criticising the North's record at the UN Human Rights Council, currently meeting in Geneva.
In a possible indication that North Korea's secretive leadership is beginning to chafe under increased pressure from the South, it was announced on Thursday that most of the South Korean officials working a joint industrial park in the North were being expelled.
South Koreans have been expelled from an
industrial park in the North [GALLO\GETTY]
Seoul's unification ministry said the expulsions were made in protest following a ministry statement last week linking further development at Kaesong with the North's progress on its nuclear programmes.
Only two South Korean maintenance officials remain at the industrial park – the most visible symbol of reconciliation set up after an historic North-South summit in 2000.
Backing the South Korean's foreign minister's warning, Rice told reporters that there had been some progress in terms of North Korea shutting down and disabling its nuclear programme, but more progress was needed.
"It is really time now for there to be movement on the declaration so that with that declaration in hand, we can move forward on the next phase," Rice said.
An accord under which North Korea agreed to abandon all its nuclear programs in exchange for economic and diplomatic benefits has been stalled by Pyongyang's failure to produce a declaration of those programmes by the end of last year.
North Korea says it gave the US a list of its nuclear programmes in November, but the US says it never received a "complete and correct" list.
Amid a flurry of diplomatic efforts, George Bush, the US president, spoke by phone with Hu Jiantao, his Chinese counterpart, on Wednesday to discuss efforts to rid the North of its nuclear weapons.
The White House said the two men pledged to continue pressing North Korea to deliver the declaration, agreed under a six-party framework.
The negotiations group is composed of the two Koreas, the US, China, Russia and Japan.
A recent sticking point in the difficult nuclear negotiations has been Pyongyang's reluctance to discuss alleged transfers of nuclear technology to other nations, notably Syria.