BRUSSELS - BELGIAN-Dutch financial services group Fortis is to write one billion to two billion euros (S$4.2 billion) off its sub-prime portfolio, Belgian daily De Standaard said on Saturday on its website.

'According to a well informed source Fortis will have to write down 1 or 2 billion euros off its subprime portfolio,' the newspaper said.

Shares in Fortis closed down over 10 per cent on Friday on market talks of profit warnings and possible exposure to US sub-prime, traders said.

A source briefed on the situation said there would be higher than announced write-offs due to Fortis' sub-prime exposure.

Fortis declined to comment on the market speculation but said it was not aware of any element that could explain the sharp fall of its shares.

A spokesman for Belgian Finance Minister Didier Reynders said he was unaware of any problems relating to Fortis.

A banking source said that Fortis was holding a board meeting on Friday. The Fortis spokeswoman declined to confirm this.

Fortis Chief Financial Officer said in November that the bank may take a 120 million euro net charge in the fourth quarter on sub-prime investments if current conditions continued. -- REUTERS