ZURICH, (Reuters)—Swiss Re said Chief Executive Stefan Lippewill take early retirement after roughly three years at the helm ina surprise move which analysts said added a new element ofuncertainty to a company Lippe had helped stabilize.

No reason was given for the departure, which Swiss Re said wouldtake effect on an as-yet undetermined date next year. Some analystssaw reinsurance chief Christian Mumenthaler as likely successor,but Swiss Re said it would look at outside as well as internalcandidates for the position.

The 56-year-old Lippe informed the Zurich-based insurer's boardover the weekend of his decision, a Swiss Re spokesman said onMonday. In a statement, Lippe cited the turnaround of theZurich-based reinsurer as the appropriate time to step down.

“The board of directors very much regrets Stefan Lippe'sdecision to retire early after almost three decades at Swiss Re,”Swiss Re Chairman Walter Kielholz said in a statement.

A successor will be appointed “soon”, Swiss Re said.

Analysts said the departure added a note of uncertainty at SwissRe after Lippe ushered in an era of greater stability following apush to take more risk under his predecessor, investment bankerJacques Aigrain.

“Lippe's leaving is a surprise and investors won't be jumpingfor joy over it,” said Bank Sarasin analyst Martin Schwab, who hasa “buy” rating on the stock.

PRIZE RATING

Lippe's main achievement was steadying the position of Swiss Re,which lost its prized AA rating in 2009 after risky investmentsjeopardized its capital base.

This prompted an emergency 3 billion Swiss franc ($3.3 billion)loan from U.S. billionaire Warren Buffett's Berkshire HathawayInc.

Swiss Re repaid the Buffett loan late last year and in Octoberwon backing from ratings agency Standard & Poor's, which liftedthe reinsurer to AA- with a stable outlook from A+.

Swiss Re said earlier this year its goal was to further improveits rating, expand its business, then return cash to shareholders.Swiss Re paid out 2.75 francs a share in 2010, up from 1 franc in2009.

As attention shifts to candidates to replace Lippe, KeplerCapital markets analyst Fabrizio Croce said Swiss Re's ChristianMumenthaler, promoted to head of reinsurance in October, is likelyto get the nod at the company, which he also saw shedding non-coreoperations.

“As a next step, we expect the company to lay off or run offAdmin Re and Corporate Solutions and focus on core competencereinsurance by promoting Mumenthaler as new CEO,” Croce said, whohas a “hold” on the stock.

“In our view, the appointment of Mumenthaler as new CEO would behighly beneficial to the company, he said.

Mumenthaler wasn't immediately available for comment.