Ackermann says to resign from Siemens supervisory board

* Josef Ackermann to step down from Siemens (TLO: SIE.TI - news) board

* Retreat follows boardroom battle over CEO succession

* Ackermann was second deputy chairman at Siemens

BERLIN, Sept 12 (Reuters) - Former Deutsche Bank Chief Executive Josef Ackermann said he would step down from the supervisory board of German engineering conglomerate Siemens , marking another retreat for one of Europe's most powerful executives.

His resignation as second deputy chairman at Siemens comes just two weeks after the Swiss national quit as chairman of Zurich Insurance (Xetra: A1JWRL - news) , following the suicide of the chief financial officer.

"I have decided to step down from the supervisory board of Siemens. I will however retain all my other board seats." he told reporters in Berlin on Thursday.

He is also a non-executive director at Royal Dutch Shell (Xetra: A0ET6Q - news) , a director at Investor AB (Other OTC: IVSBY - news) , the investment company founded by Sweden's Wallenberg family, and a member of the board of directors at private equity firm EQT.

In June, Ackermann clashed with fellow Siemens directors during a tussle over whether to oust Chief Executive Peter Loescher.

When supervisory board chairman Gerhard Cromme pushed for Loescher to be removed immediately, Ackermann was among the few executives on the board to dissent. Siemens named finance chief Joe Kaeser to replace Loescher soon thereafter.