By Katharina Bart

ZURICH (Reuters) - Josef Ackermann, the chairman of Zurich Insurance <ZURN.VX> and former Deutsche Bank boss <DBKGn.DE>, resigned on Thursday over the apparent suicide of the insurer's chief financial officer, further roiling the top ranks of the firm.

Ackermann said the family of Pierrer Wauthier, who worked at Europe's No. 3 insurance group for 17 years, believed he shared some of the blame for his death.

"I have reasons to believe that the family is of the opinion that I should take my share of responsibility, as unfounded as any allegations might be," he said in a statement on Thursday.

"As a consequence, I see the possibility of a continued successful board leadership to the benefit of Zurich called into question," he said.

On Tuesday, police said Wauthier - found dead at his home in a lakefront suburb of Zug outside Zurich on Monday - appeared to have committed suicide.

A spokeswoman did not elaborate on what allegations Ackermann was referring to surrounding Wauthier, who leaves behind a wife and two children.

Vice-chairman and former ABN Amro banker Tom de Swaan will take over as acting chairman, the insurer said.

Zurich's top ranks have seen considerable change in the last 12 months: former general insurance head Mario Greco left in mid 2012 to become head of Italian insurer Generali <GASI.MI>. Two weeks ago the head of its life insurance arm, Kevin Hogan, left to become AIG's <AIG.N> head of consumer insurance.

"When the chairman leaves after you've already lost your head of global life, Mario Greco, and then the unexpected loss of Pierre Wauthier as CFO, it will lead to more uncertainty," Helvea analyst Daniel Bischof said. He rates the stock at buy with a 265 franc target price.

On August 15, Zurich said it would be hard pressed to meet certain performance targets after posting a 27-percent fall in second-quarter net profit due to natural disaster payouts, which topped those of European rivals because of its high exposure to the United States.

Wauthier's death and the apparent suicide of Swisscom <SCMN.VX> boss Carsten Schloter five weeks ago have prompted calls for greater support for boardroom high-fliers.

Since returning to Switzerland after leaving Deutsche in 2012, Ackermann has become a forceful advocate for the Swiss financial sector. He is one of few senior industry figures to keep his job through the financial crisis.

(Editing by Louise Ireland)