OSLO, Norway (AP) _ The chief executive of Statoil, Norway's biggest company, resigned Tuesday as the oil giant said it was cooperating with a police investigation into whether it made improper payments while trying to expand into Iran.

Olav Fjell, 52, was the third Statoil executive to leave in a week. He is being replaced by chief financial officer Inge Ketil Hansen, a 57-year-old business economist with broad management experience, as acting CEO.

``We had a discussion and agreed that this was the best solution,'' Fjell said as he was escorted from Statoil's offices in the capital, Oslo, in the rain early Tuesday, a security guard holding an umbrella over him.

Late Sunday, chairman Leif Terje Loeddesoel resigned, citing the controversy over whether the company acted improperly by hiring Iranian-operated Horton Investment Ltd. under contract for $15 million to help it develop business deals in Iran.

Fjell terminated the contract with Horton last week and Statoil's head of international exploration and productions, Richard J. Hubbard, resigned at that time.

Statoil's board of directors was criticized by labor unions for keeping Fjell on board despite the deal.

Earlier this month, Norway's economic crime unit Oekokrim raided the state-controlled company's headquarters in Stavanger, seeking evidence to determine whether the contract involved corruption. Oekokrim has not said if it found any improprieties.

In a statement, Statoil's board hoped Fjell's departure would ``normalize the situation in the company.''

``I think it's sad that such a case involving ethics would be my fate,'' Fjell, 57, said after his resignation after four years as head of Norway's biggest company. He also resigned as chairman of the board of NSB, the state-run railroad.

Board member Kaci Kullmann Five said that the company examined the deal and was cooperating with the investigation, but refused to elaborate.

Kullmann Five said the nine-hour meeting that ended in the early hours of Tuesday reviewed new details, including reports by Statoil's internal watchdogs, but she refused to reveal what those details were.

However, she said the new revelations directly led to the eight-member board's decision to ask for Fjell's resignation.

Kullmann Five said Statoil wants to maintain the same high ethical standards abroad as would be expected of it while working at home in this Nordic country of 4.5 million people.

``It is fully possible for the group to succeed internationally without becoming involved in activities which lie in a borderland as regards ethical norms and rules,'' she said.

Last week, Loeddesoel, as chairman, said the board still had faith in Fjell, partly because there was no proof yet that any money had been misspent.

That wasn't enough for Norway. Five days later, Loeddesoel was gone from his Statoil post, followed by Fjell.

The market had expected Fjell's resignation. Trading in Copenhagen, Statoil shares were down 7 cents to close at $8.85.

Statoil, which was founded by the government in 1972, is seeking to expand internationally. Norway produces about 3 million barrels of oil, plus natural gas, making it the world's third-largest oil exporter after Saudi Arabia and Russia.

Kullmann Five, speaking for the board, said Statoil wants to maintain the same high ethical standards abroad as would be expected of it while working at home in this Nordic country of 4.5 million people.

``It is fully possible for the group to succeed internationally without becoming involved in activities which lie in a borderland as regards ethical norms and rules,'' she said.

Statoil was partly privatized in 2001 when the state sold 17.5 percent of its shares to investors.

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