Speaking at a news conference with US Secretary of State Condoleezza Rice, he said North Korea must meet its commitment to provide a complete and correct declaration of its nuclear activities, which was promised for the end of last year.
'Time and patience is running out. We hope North Korea will submit a declaration as soon as possible so as not to lose good timing,' he said in his first trip to Washington as South Korea's foreign minister.
The Bush administration's term ends in January 2009 and while Mr Yu did not mention this, US allies are becoming increasingly conscious of the US political timetable.
Mr Yu did not indicate what, if any, ultimatums might be issued to the North Koreans, or whether the major powers dealing with the issue might offer more inducements.
The 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 programs by the end of last year.
The so-called six-party agreement was made between the two Koreas, China, Japan, Russia and the United States.
US President George W. Bush spoke to Chinese President Hu Jintao on Wednesday over North Korea, White House spokeswoman Dana Perino said in a statement.
'The two presidents pledged to continue to work closely with the other six-party partners in urging North Korea to deliver a complete and correct declaration of all its nuclear weapons programs and nuclear proliferation activities, and to complete the agreed disablement,' MS Perino said.
Rice: Time for movement
Dr Rice said there had been some progress in terms of North Korea shutting down and disabling its nuclear reactor in Yongbyon, but they needed to go further.
'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,' she said.
A recent sticking point in the declaration had been Pyongyang's reluctance to discuss any transfer of nuclear technology to other nations, notably Syria, as well as its suspected pursuit of uranium enrichment.
Asked whether the Syrian issue was holding back the North Korean declaration, Dr Rice declined to be drawn specifically on the cause of the delay.
'We expect that the declaration and any associated documents will show the full range of the North Korean programs and activities,' Dr Rice said.
'It was supposed to be completed on Dec 31st. I am not one to say that exact deadlines are that important - to get it right is more important. But I completely agree with the minister, we have been at this for quite a long time,' said Dr Rice, signalling US impatience.
She reiterated the United States was ready to meet its own obligations under the six-party agreement, which includes a range of benefits for North Korea if it gave up its nuclear programs.
These include the prospect of normal ties with the United States and the rest of the world, humanitarian aid and fuel oil. The United States has also held out the possibility of dropping North Korea from its list of state sponsors of terrorism and easing sanctions. -- REUTERS