10:03 PM UK, Monday March 14, 2011

The plea comes after water levels were restored in the ailing reactor, but the rods remained partially exposed - increasing the risk of radiation and a potential meltdown.

The former deputy director of the International Atomic Energy Agency (IAEA) told Sky News that the status of the unit 2 reactor may deteriorate even more. "I think the situation is still very, very grim - we are by far not over the worst," Olli Heinonen said.

Meanwhile, France's ASN nuclear safety authority said the nuclear accident in Japan could be classed as level 5 or 6 on the international scale of 1 to 7 - on par with the 1979 US Three Mile Island meltdown.

Sky News' Anna Botting, in Sendai, says the authorities are warning people not to drink tap water and to take iodine to help prevent the threat of thyroid cancer.

Specialists are now considering spraying water directly on the hermetically-sealed container in an attempt to cool it.