The United States and North Korea probably won't reach an agreement in talks this week on opening the communist state's secretive nuclear program to international inspections, the top U.S. negotiator said Thursday.

Technical experts from both countries, meanwhile, met for five hours Thursday on the most urgent issue in the nuclear standoff: what to do with 8,000 spent nuclear fuel rods corroding in a cooling pond near the capital, Pyongyang.There was no immediate comment on any progress. But several sources, who refused to be identified, said there were good prospects for an agreement to slow the corrosion and buy time for wider talks.

North Korea's refusal to let monitors inspect its nuclear sites has fueled suspicion that Pyongyang is developing nuclear weapons, despite its denials.

On Wednesday, chief negotiators Robert L. Gallucci and Kang Sok Ju abruptly canceled a scheduled evening session without explanation and left further negotiations to technical experts.

The cancellation led to speculation of a hitch in the talks, but sources said the main reason the political talks were adjourned was to let the experts iron out technical details.

Gallucci, an assistant secretary of state, told Japan's Kyodo news agency Thursday that he did not expect North Korea to agree during the current round of talks to open its nuclear program. But he said he hoped to narrow differences.

Central to the talks are the spent fuel rods. Pyongyang says it needs to begin reprocessing them by the end of the month before they start to give off harmful radiation. Western experts say reprocessing would leave North Korea with enough plutonium for five nuclear bombs.

Gallucci told Japanese reporters that the two sides were still discussing a proposal to send a team of international nuclear experts to help North Korea stabilize the corroding rods. The United States, he said, still wants a third country to reprocess the rods so North Korea cannot secretly extract plutonium.

The U.S. mission expects the current round of talks to conclude by Friday evening.

North Korea provoked a crisis earlier this year by removing the rods from its Yongbyon nuclear plant in defiance of the U.N. nuclear watchdog, the International Atomic Energy Agency. The United States has put a threat of sanctions on hold pending the outcome of the negotiations.

U.S. negotiators want guarantees that North Korea will open up all nuclear facilities to inspection in return for diplomatic ties and technical aid.

But though North Korea has complied with some checks, it refuses to accept full inspections.