Norway was accused of authorising the "mass slaughter" of its endangered wolf population on Friday after announcing that 47 of the predators would be killed by hunters.

The move, which follows previous efforts to control the population, was hailed by farmers but condemned by outraged environmental groups.

Only 65-68 wolves were registered last winter in Norway, according to the specialised body Rovdata, but their numbers will have increased after the birth of an unknown number of pups in April and May.

At least another 25 wolves were observed in the border region with neighbouring Sweden last winter.

"This is pure mass slaughter," blasted Nina Jensen, the head of the Norwegian branch of the World Wide Fund for Nature (WWF).

"We haven't seen anything like this in almost 100 years, when the policy at the time was to exterminate all the big predators," she added.

Farmers complain regularly about wolves attacking their sheep.

"We find the reason (for the killing) justified and intelligent, especially the potential damage that these wolf packs represent to farming," Erling Aas-Eng, a regional official for a farming association, told broadcaster NRK. 

Without setting an exact overall number of wolves allowed, the Norwegian parliament agreed in early June to limit the number of litters to between four and six per year, including at least three for the Norwegian wolf population and the rest in the cross-border packs.

The Norwegian wolf population currently has seven packs with one reproductive couple, which is "above the national population target" since each pack can be expected to deliver a new litter every year, the Norwegian environmental agency said.

Wolves are listed as "critically endangered" on the 2015 Norwegian list of endangered animals.