Sochi's Olympic biathlon course is the toughest in the world, according to billionaire Mikhail Prokhorov, president of the Russian Biathlon Union.

The course at the Psekhako Ridge near Krasnaya Polyana is undergoing its first serious test event for the 2014 Games, with 120 athletes from across the country competing in the Cup of Russia.

Prokhorov said the peaks and troughs in the course have a vertical range of 60 meters, making it the world's most exhausting biathlon.

"It's the most difficult course in the world," said Prokhorov, who is also a Russian presidential candidate in the elections next month.

"The temperature differential in the snow is 4 degrees Celcius. We don't have this anywhere else in the world. For the ski lubricators, for the people who prepare the skis, this is a huge problem. But this makes the competition all the more unpredictable," said Prokhorov, a keen exponent of the sport who has been the union's president since October 2008.

The Cup of Russia is closed to the public because of construction delays at the spectator facilities. When completed, the course will have a 9,600-seat stadium billed as one of the most advanced ever built.

Prokhorov, also owner of the New Jersey Nets NBA basketball team, noted the lack of crosswinds at the course's firing range, minimizing the element of chance during competition.

"We won't have a lottery here," he said.

The course carved into Mount Kenashi for the 1998 Nagano Games had a reputation as one of the world's hardest.