OSLO, June 5 (Reuters) - Norwegian oil companies have agreed to a wage deal with three labour unions, preventing any strike action that would have disrupted output, unions and companies said on Friday.

Labour unions had said nearly 8% of Norwegian offshore oil and gas workers planned to strike if wage mediation failed, and the industry estimated that this would have cut output by an initial 45,500 barrels of oil equivalent per day.

A strike could also have been expanded at any time, with significant impact on production, union officials had warned.

Norway produces more than 4 million barrels of oil equivalent per day, almost equally divided between crude and natural gas, and any reduction could impact markets at a time when Middle East output is curtailed by the Iran war.