OSLO- The natural gas output capacity at three Norwegian offshore fields was cut by a combined 43.5 million cubic metres per day on Sunday due to unplanned outages, pipeline system operator Gassco said.

Norway is Britain's largest external gas supplier, and the second largest of Europe after Russia, normally exporting around 330 million cubic metres per day.

The partial outages at Equinor's Troll, the country's largest gas field, as well as at the Visund and Kvitebjoern fields were caused by processing problems, and the expected duration remained uncertain, Gassco said.

Impact on production at the three fields, which have a combined output capacity of more than 140 million cubic metres per day, was also uncertain, it added.

An Equinor spokesman said any updates would be provided by Gassco.

Nordic power bourse Nord Pool Spot separately reported that the onshore Kollsnes facility, which processes gas from the fields, saw a drop in power consumption.

British wholesale gas prices rose on Friday as a forecast for colder temperatures boosted demand, while domestic supply remained curbed by maintenance. 

(Reporting by Nerijus Adomaitis, editing by Terje Solsvik) ((nerijus.adomaitis@thomsonreuters.com; +47 9027 6699; Reuters Messaging: nerijus.adomaitis.thomsonreuters@reuters.net))