Hopes appeared to be fading for talks with North Korea on the sidelines of a regional security forum in Malaysia.
North Korea raised regional tension with missile tests on 5 July
Officials from five countries involved in stalled talks with Pyongyang are at an Association of South East Asian Nations (Asean) forum in Kuala Lumpur.
But a North Korean spokesman said the US had first to lift financial sanctions before talks could go ahead.
US Secretary of State Condoleezza Rice has arrived from the Middle East, where she has been trying to broker a deal.
The growing crisis in Israel and Lebanon is also expected to be high on the agenda at the Asean talks.
The North Korean Foreign Minister Paek Nam-sun is in Malaysia, along with officials from the other five nations involved in multilateral dialogue with North Korea over its disputed nuclear programme.
The forum comes amid heightened concern over the North Korean issue in the wake of its missile tests of 5 July, and the five parties - the US, Russia, China, South Korea and Japan - have been seeking informal talks.
But a North Korean spokesman, Jong Song-il, said six-party talks "cannot happen".
"So go tell the Americans to lift the financial sanctions if they want to see the six party talks at an early date," he said.
Earlier this week, North Korea's state news agency KCNA accused Ms Rice of reacting like a "political imbecile" to its missile tests.
North Korea called Ms Rice a political imbecile
US nuclear negotiator Christopher Hill said North Korea had shown "no interest" in a meeting. "Five parties are ready, it's just the sixth is somehow lost on the way," he said.
A Japanese spokesman also cast doubt on any progress. "Japan is making efforts, China is making efforts," Yoshinori Katori said. "But we still don't know at this stage."
Officials from eight countries - the five parties plus Australia, Malaysia and Canada - are set to meet on Friday when the Asean Regional Forum opens as an alternative to formal talks with the delegation from Pyongyang.
"The eight countries will exchange views on regional issues that they are concerned about," Chinese foreign ministry spokeswoman Jiang Yu said.
A number of bilateral meetings have already taken place, including one between the Chinese and Japanese foreign ministers.
Efforts to end the fighting in the Middle East are also expected to feature high on the agenda for the talks.
On Wednesday, the ten-member Asean group condemned Israel for its attack on a UN post in Lebanon in which four UN observers were killed.
In a separate development, Iran's Foreign Minister Manouchehr Mottaki is also in Kuala Lumpur.
He will meet Malaysia's Foreign Minister Syed Hamid Albar to discuss the tension in the Middle East, a Malaysian official said.
But he will not meet Ms Rice, Mr Hill said, adding his visit was a bilateral arrangement with Malaysia. "It has nothing to do with Secretary Rice," he said.