The Tour is part of the International Ski Federation's Cross Country World Cup circuit with Østberg's victory gaining her a place at the top of the overall standings.

Two-time Olympic champion Østberg finished first in the women's 10 kilometre race with a time of 32min 8.9sec, just one tenth of a second in front of Russia's Natalia Nepryeva.

Russia also claimed third spot through Anastasia Sedova, who crossed the line a more comfortable six seconds behind Østberg.

Prior to today's action Jessica Diggins from the United States held the overall lead, but an 11th placed finish today in a time of 33:07.3 has seen her drop to fourth overall.

It means after four stages Østberg now leads with an overall time of 1 hour 5.6min, 24.1 seconds in front of Nepryaeva.

Sweden's Stina Nilsson, who won the last sprint stage in Val Muestair, finished 10th today and sits eighth overall.

On the men's side Iversen won the 15km race in a time of 45:30.3, just under a second in front of Italy's Francesco De Fabiani.

The result means Iversen, who also won the same race in Oberstdorf last year, is now up to third in the overall Tour de Ski rankings.

Taking third spot in today's race was Russia's Sergey Ustiugov, who finished in 45:32.3, exactly two seconds behind Iversen.

However, even though he could only finish ninth today, Norway's triple Olympic champion Johannes Høsflot Klaebo maintains the overall lead thanks to his wins on both sprint stages.

He has a time of 1:20:08.0.

Stage five will go ahead tomorrow in the same resort, with pursuit races for both men and women, before the final two stages will both take place in Val di Fiemme in Italy on January 5 and 6.

Østberg has also taken over the overall World Cup lead from compatriot Therese Johaug, while Russia's Alexander Bolshunov still tops the men's standings.