(Adds comment from Nordea CEO, additional quotes from FSA)
STOCKHOLM, April 4 (Reuters) - Sweden's Financial Supervisory Authority (FSA) has contacted authorities in Luxembourg for information related to allegations that Nordea , the Nordic region's biggest bank, helped some clients set up accounts in offshore tax havens.
The allegations against Nordea appeared in a leak of more than 11.5 million documents from the files of law firm Mossack Fonseca, based in Panama.
While setting up offshore accounts is not necessarily illegal it could be in breach of Swedish money laundering rules. Nordea was found to have breached such rules last year and was fined the maximum 50 million crowns ($6.1 mln) and handed a severe warning by the FSA.
"We take this extremely seriously," said Christer Furustedt, head of the FSA department that oversees major Swedish banks.
"If the media reports are correct and they set up complicated structures to hide the actual beneficial owner then that is hardly in line with the rules," he said.
Nordea said in a statement it would review all activities relating to offshore accounts in Luxembourg.
The bank said it strongly denounced tax evasion and had taken proactive measures since 2009 to ensure all customers' holdings and income on their accounts were reported to the tax authorities.
"However, we regret that we didn't have these procedures already earlier," Nordea CEO Casper von Koskull said.
The FSA fined Nordea in May 2015 and said the bank had severe shortcomings in its approach to combatting money laundering and that a case could even be made for revoking Nordea's banking licence.
For other stories on the Panama Papers leak, click on ($1 = 8.1424 Swedish crowns)
Reporting by Johan Ahlander and Simon Johnson; Editing by David Goodman and Susan Fenton