BP Plc breached a plethora of rules and regulations which led to a fire, a difficult response and a nine-and-a-half week shutdown at its Valhall facility off Norway last year, an official investigation concluded on Thursday.

Petroleum Safety Authority Norway said BP's lack of maintenance, deficient maintenance management, inadequacies in risk identification and poor barrier management could have had devastating consequences in the July 13 incident.

Under slightly different circumstances ... it could have escalated and created a serious position on the installation, with personal injuries or loss of life, the watchdog said in a statement.

BP, whose safety record was tarnished in the Deepwater Horizon incident and resulting oil spill, said it would comply with the watchdog's recommendations.

We have done some adjustments already on maintenance routine and management. We have a deadline of February 1 to establish a binding plan to make the improvements, which have to be implemented by July 1, BP said in a statement.

We will meet the deadlines and we have implemented a group to carry out all the improvement measures, it added.

The explosion on the Deepwater Horizon rig in April 2010, which killed 11 workers and spewed more than 4 million barrels of oil into the Gulf, has sparked a slew of lawsuits and federal citations against the companies involved.

The July 13 fire at Valhall, in Norway's part of the North Sea, led to the evacuation of hundreds of workers and supported oil prices as the field contributes to a crude oil stream used in the global Brent price benchmark.

The Norwegian watchdog can issue recommendations and orders but has no authority to issue fines.

(Reporting by Balazs Koranyi; Editing by David Holmes)