The chief executive of the embattled Swiss bank UBS, Oswald Grübel, has quit after the bank lost an estimated $2.3bn (£1.5bn) in the alleged rogue trading scandal.

Sergio Ermotti, the bank's head of Europe, Middle East and Africa, will take over as CEO for now.

The bank said it had accepted Grübel's resignation and paid "testimony to his uncompromising principles and integrity".

The board said in a statement it had asked management to accelerate an overhaul of the investment bank already under way "concentrating on advisory, capital markets, and client flow and solutions businesses".

UBS's board meeting, one of four regular meetings per year, had originally been due to end on Friday ahead of the UBS-sponsored Singapore Formula One Grand Prix on Sunday, when executives will be trying to reassure big clients.

But deliberations continued by conference call after the board left Singapore, with some members heading back to Switzerland.

The 67-year-old German, brought out of retirement to try to salvage UBS in 2009, refused to comment to reporters as he left the lengthy meeting which had been scheduled to finish on the Friday.

An AFP reporter on the scene said Grübel made no response when asked, "Were you fired?" and, "Did you lose your job?"

He came under heavy fire over alleged unauthorised trading by Kweku Adoboli, the 31-year-old charged with fraud and false accounting at UBS.

Adoboli has been remanded in custody and has not entered a plea to the four charges.