A senior Democratic senator said Sunday that negotiators had made progress in getting North Korea to halt its nuclear programs when they reached a pact on Tuesday, but that the agreement left key issues unresolved. The disarmament deal reached among North and South Korea, China, Japan, Russia and the United States requires Pyongyang to seal its main nuclear reactor, allow international inspections and begin accounting for other nuclear programs within 60 days. In return, North Korea will receive 50,000 tons of heavy fuel oil, a down payment on a promised 1 million tons in oil or aid of a similar value if it ultimately disarms. Sen. Carl Levin said the pact did not address allegations that North Korea is operating a secret uranium enrichment program. "We don't know about the uranium," he said on a television news program. "We haven't got a commitment on that secret program yet."