Norwegian energy company Statoil said it was in a state of mourning after 13 employees died when a helicopter crashed after leaving an offshore platform.

An Airbus helicopter H225 Super Puma, formerly known as a Eurocopter EC225, crashed last week off the coast of Norway after picking up passengers from a Statoil oil platform. The group on board included 11 Norwegians, one Italian and one British citizen, according to authorities. All were employees of Statoil.

Statoil President and CEO Edlar Saetre said in a statement the company was in a state of mourning after what he described as one of the worst accidents ever to hit the Norwegian oil industry.

"We are one family," he said. "We will stand together as one united industry, and do everything in our power to take care of the affected families."

The helicopter was en route from the Gulfaks B platform at the time of the incident and Statoil said it has since suspended oil production there in order to "take care of the staff in the best way possible.

Statoil said it started its own investigation in cooperation with safety representatives and company employees.

A formal national investigation is under way. The Petroleum Safety Authority of Norway mobilized its response team shortly after Friday's crash, but said that, since it was not responsible for aviation safety, its statements would be limited.

"Finding an answer to why the helicopter crashed is very important," Saetre said.

Statoil said it was marking the tragedy with a minute of silence. All flags will be flown at half-mast Monday.

Statoil workers were among those killed in a terrorist attack on the In Amenas natural gas facility in eastern Algeria in January 2013.