Seoul: North Korea appears almost certain to miss a deadline in a nuclear deal, a development that is unlikely to scuttle the disarmament-for-aid pact it reached with regional powers but could hamper its implementation.

Pyongyang has met one part of the deal by starting to take apart its Soviet-era nuclear facility that produces arms-grade plutonium, but is unlikely to meet its obligation to fully account for its nuclear activities by the end of the year.

The United States and South Korean officials have called on the North to say how much plutonium it has produced - about 50kg by US estimates - and answer US suspicions of having a secret programme to enrich uranium for weapons. "We are at a crucial moment," South Korean Foreign Minister Song Min-soon told reporters on Friday.

South Korea, which is loath to put pressure on the North, is not now thinking of any punishments if the deadline is breached.

North Korea missed a separate deadline, without retributions, earlier this year to freeze its Yongbyon nuclear plant due to a dispute over its international finances. It eventually lived up to its obligations once the row was settled.

North Korea has been cooperating in disabling its three main nuclear facilities - an ageing reactor, a plant that makes nuclear fuel and another one that turns spent fuel into arms-grade plutonium, US and South Korean officials have said.

November action

The process, started in November, is the first tangible action North Korea has made to take apart its nuclear weapons programme since it began its quest for the weapons in earnest in the 1980s. If it lives up to the deal it reached with China, Japan, Russia, South Korea and the United States, the destitute state would receive 1 million tonnes of heavy fuel oil or equivalent aid and the US would take it off its terrorism black list.

A uranium enrichment programme could provide North Korea, which has ample supplies of natural uranium, another way to produce fissile material, but experts do not think it has anywhere near a full-scale enrichment programme.