ELVERUM, Norway, April 15 (UPI) -- Conservationists and police in Norway plan a campaign against farmers who have killed wolves by blowing up their lairs and putting out poisoned bait.

In one recent incident, Kenneth Larsen of Hedmark University College spent a week trying to find a female wolf he had tracked before, Aftenposten reported. When he returned to his car after a fruitless search, he found that three of its tires had been slashed.

Researchers blame half the deaths of wolves in Scandinavia on illegal hunting, mostly by farmers who say the wolves attack livestock.

Knut Maelen of the Hedmark Police District said that the tire slashing is another sign of an "inflamed situation."

Petter Wabakken of Hedmark University College said that rural areas in Hedmark County, which lies along the Swedish border in southern Norway, have the highest rate of wildlife crime in Norway. He and his colleagues have found evidence of both poison and of explosives being used on lairs, he said.