Norway's agriculture ministry said the levels described by the Russians would be poisonous but are so high they are almost unbelievable.

"Our angle at the moment is that there must be some mistake," Reidunn Agarthe Medhus, an adviser to the ministry, said.

Between January and October Norway exported salmon worth 1.4 billion Norwegian crowns ($206.3 million) to Russia, a 60 percent increase from last year, out of global sales of 10.5 billion Norwegian crowns.

Norway monitors the levels of lead and cadmium in its salmon, which can absorb the metals from fish feed used by farms, and this year there has been only one case of excessive levels, Medhus said.

But Russian vets found lead 18 times higher and cadmium 3.5 times higher than its safety levels in salmon from four Norwegian fish farms, a statement from Moscow's agriculture ministry said on Thursday.

It said it would ban salmon from those farms from Monday Dec. 5.

"Prospects of reinitiating imports from the farms...may be examined after they are inspected jointly by veterinary service exports of Russia and Norway," the Russian ministry said.

Russia is the world's biggest importer of Norwegian salmon and as its middle class expands and logistics improve demand continues to boom.

Norwegian diplomats are waiting to meet their Russian counterparts, Ingellis Jacobsen, Norway's seafood marketing manager in Russia, said from its embassy in Moscow.

"We are trying to get meetings and get all the facts on the table," she said.