North Korea is reported to have refused entry to international inspectors checking the use of fuel oil supplied under a key nuclear deal.

The move appeared to be a reprisal for a United States-led decision to stop providing the unpredictable North with fuel oil, amid mounting tension over the country's nuclear weapons ambitions.

It is high time to decide upon who is to blame for the collapse of the framework

North Korean Foreign Ministry statement

It came as America's CIA warned that North Korea has the capacity to produce "several more" nuclear weapons, apart from the one or two it is already believed to possess.

Diplomats in Japan said North Korea's decision to bar the inspectors had been conveyed in a letter to the international consortium supplying the oil, the Korean Peninsula Energy Organisation (KEDO).

KEDO has provided North Korea with fuel oil in exchange for the freezing of its nuclear programme since 1994, under a deal known as the Agreed Framework.

Fears of crisis

Shipments were halted last week after Pyongyang allegedly admitted to have a nuclear weapons programme, thereby violating the accord and the Nuclear Proliferation Treaty.

KEDO had planned to send officials next week to Pyongyang for a routine inspection to make sure that a November shipment that had already arrived by tanker from Singapore was being used to generate electricity.

If the North does refuse entry to the monitors, it would call the accord's future into serious doubt and raise the spectre of another nuclear crisis on the Korean peninsular.

The North has already accused the US of collapsing the accord, though it is not clear how far its angry words were rhetoric.

The North Korean Foreign Ministry said in a statement on Thursday that Pyongyang regarded the suspension of oil deliveries as "a wanton violation" of the accord.

"Now that the US unilaterally gave up its last commitment under the framework, the DPRK (North Korea) acknowledges that it is high time to decide upon who is to blame for the collapse of the framework," a North Korean spokesman was quoted as saying by the state-run news agency KCNA.

North Korea had been receiving 500,000 tons of heavy oil a year from KEDO.

CIA warning

The US says North Korea admitted to US special envoy James Kelly in October that it had a programme for producing highly enriched uranium - a key ingredient in nuclear weapons.

North Korea has never publicly confirmed or denied having nuclear weapons.

But America's CIA said on Thursday that North Korea had the capacity to make more nuclear weapons than the one or two it is already believed to possess.

The CIA said spent fuel from a nuclear reactor shut down under the 1994 accord could be used to make between one and six more bombs.

The enriched uranium programme which the North allegedly admitted to in October could provide "two or more" bombs each year by "mid decade", the report said.