* Probe focuses on a 2009 deal involving $42 mln loan
* TGS-Nopec says cooperating fully with enquiry
* Shares in TGS-Nopec fall (Adds detail from police, quotes by TGS-Nopec CFO)
OSLO, May 6 Norwegian police raided the offices of seismic surveying company TGS-Nopec near the capital Oslo on Tuesday and charged it with violating tax and securities trading laws.
The police are investigating a 2009 contract between TGS-Nopec, which maps the seabed for oil and gas deposits for energy firms, and a company called Skeie Energy AS, later known as E&P Holding AS. The deal involved a convertible loan of $42 million.
"(Police) today presented a criminal charge against TGS for violation of the Norwegian Tax Assessment Act and the Norwegian Securities Trading Act," the company said in a statement.
"In connection with the criminal charge, (police) today visited the offices of TGS in Asker with a search warrant to investigate the matter."
TGS-Nopec shares fell from 209 Norwegian crowns ahead of the announcement to 204.6 crowns shortly after. By 0712 GMT they traded at 206.6 crowns.
Police told Reuters they raided several companies as part of the investigation and arrested several people. They declined to say who was arrested or which companies were involved.
"The persons and companies are charged with severe tax fraud and being accessory to it. One of the companies is also accused of market manipulation," police lawyer Marianne Bender told Reuters. "We are in the early stages of the investigation."
TGS-Nopec said it was "fully cooperating". Chief Financial Officer Kristian Johansen said none of the people arrested were working at TGS-Nopec, as far as he was aware.
"They question the rationale of the contracts, but I can't say more," he said.
TGS-Nopec took an impairment charge of $19.5 million in 2012 as it wrote down the value of its interest in E&P Holding Group.
It also agreed that, as part of a agreement over a restructuring of E&P Holding, it would convert some its outstanding loan to equity.
E&P Holding was not immediately available for comment. (Reporting by Henrik Stolen and Balazs Koranyi; writing by Gwladys Fouche; editing by Tom Pfeiffer)