A top U.S. envoy said Friday he expects next week's negotiations aimed at ridding North Korea of atomic weapons to be tough.

Pyongyang agreed last year to disable its nuclear reactor under a disarmament-for-aid pact. But it recently denied having agreed to allow inspectors to take samples from its nuclear complex to verify past nuclear activities. Negotiations have stalled over how to check that accounting.

"I'm sure the negotiations will be, as usual, difficult," Assistant Secretary of State Christopher Hill told reporters after he wrapped up two days of preliminary consultations with North Korean Vice Foreign Minister Kim Kye Gwan in Singapore.

Hill said the two diplomats' discussions focused on trying to establish a way to verify the detailed accounting that the North Korea submitted in June.

"We talked a lot about the verification issues today," Hill said.

State Department spokesman Robert Wood told reporters in Washington that the United States was hopeful it would get a final verification protocol during international talks that begin in Beijing on Monday.

Hill will travel to South Korea on Saturday before talks with Japan, China, South Korea and Russia that being on Monday.