Story highlights An agricultural cooperative says low-carb diets could be to blame

The cooperative also says milk production has decreased this year

An online auction site offers butter at 30 times the normal price

Authorities have responded by reducing the tariff on milk product imports

Norwegians are facing an unexpected wrinkle in their Christmas cooking plans. Butter supplies are scarce, and prices have skyrocketed.

A higher demand for butter as a result of low-carb diets and increased interest in natural, home-cooked meals is one reason for the shortage, according to Tine, the country's largest farmer-owned dairy cooperative.

A rainy summer reduced the quality of animal feed, decreasing milk production in Norway this year by 20 million liters (5.3 million gallons) compared with the same period last year, the cooperative said.

The Norwegian government has responded to the crisis by reducing tariffs on milk product imports, the country's agricultural authorities said.

But many stores have been rationing how much butter they sell.

One seller on a Norwegian auction website offered 500 grams (1.1 pounds) of butter Tuesday for roughly 30 times the normal price.

Authorities detained a Russian citizen Monday who they said was trying to smuggle 90 kilograms (200 pounds) of butter from Germany into Norway. Food safety authorities then warned people not to buy butter from strangers, Norway's TV2 reported.

Danish airports and ferries traveling between Norway and Denmark have started offering butter in their duty-free shops, according to press statements.

Some Norwegian politicians have criticized the government for acting too slowly, and right-wing bloggers have compared the government's agricultural policies -- which include high tariffs on milk product imports -- to those of former Soviet states.

Others have taken a more light-hearted approach to the problem. Norwegian and Danish television recently broadcast live coverage of Danes handing out 2,000 kilograms of free butter to Norwegians on the streets of Oslo.