SEOUL, March 18, 2009 (AFP) - North Korea has slowed down work to disable its plutonium-producing atomic plants amid a deadlock in six-party nuclear disarmament talks, a Seoul official said Wednesday.

"North Korea is slowing down the pace of removing the spent fuel rods from the nuclear power plant as part of disablement," an official involved in the talks told AFP.

"It is now removing 15 nuclear fuel rods a week, down from 15 a day last autumn," he said on condition of anonymity.

A six-nation deal promises the North one million tons of fuel oil or equivalent energy aid in return for the disabling of its Yongbyon complex, which produced weapons-grade plutonium from the spent rods.

Analysts estimate the North may in the past have produced enough plutonium for half a dozen bombs, in addition to the device it tested in October 2006.

The last round of talks -- involving the two Koreas, the United States, China, Russia and Japan -- ended in stalemate in December because of failure to agree ways to verify the North's declared nuclear activities.

The US State Department said afterwards there was an "understanding" that no more energy shipments would be made without a deal on verification. The North reportedly responded that disablement work would be slowed accordingly.

Despite the US claim, some energy shipments went ahead but the full amount has not been delivered. Japan refuses to provide its share until the North settles a separate dispute on Japanese abductees.

The new US envoy on North Korea, Stephen Bosworth, visited Northeast Asia this month for talks aimed at restarting the six-party talks. He said he was hopeful the process could resume relatively soon but gave no timeframe.