A U.S. envoy says that three days of talks have failed to bridge a dispute with Pyongyang over how to have North Korea verify its past atomic activities.

Christopher Hill said Wednesday just before flying out of Beijing that North Korea would not agree to proposals made by the other countries.

North Korea is refusing to allow outside inspectors to take samples from its main nuclear complex at Yongbyon — a crucial method of checking whether it has been truthful in its accounting of its nuclear programs.

The talks involving the U.S., the two Koreas, Japan, Russia and host China began Monday, but remained at an impasse over how to impose a verification process acceptable to all parties.