Copenhagen Re will not underwrite new reinsurance business for the 2001 to 2002 renewal season.
The global reinsurer originally suspended underwriting on 25 September to assess its exposure to the US World Trade Centre losses.
It was subsequently downgraded by ratings agency AM Best from A- (excellent) to B++ (very good). In October, Copenhagen Re announced it was seeking a new capital provider to inject money to write more business next year.
Now it has stopped taking on new risks during the 1 January renewal season.
It is thought 25 staff from its Denmark office have been made redundant. A further 75 from its parent company, the Danish mutual insurer Alm Brand, are also reported to have lost their jobs.
Copenhagen Re has also raised its estimate of losses arising on 11 September from DKr350m (£29.5m) to DKr700m (£59m).
In a statement to the market, it said: "There is substantial uncertainty as to the volume of claims resulting from the World Trade Centre.
"Copenhagen Re's share of the losses remains subject to uncertainty and may still be adjusted upward or downward. More specific estimates probably cannot be made until 2002."