Oswald Gruebel resigned on Saturday as chief executive of troubled Swiss bank UBS, saying he took the blame for the $2.3 billion loss run up in alleged rogue trading in its investment banking division, Reuters reported. The bank, which said it would beef up risk controls under an accelerated restructuring of that part of its business, named its Europe, Middle East and Africa head Sergio Ermotti -- only at UBS since April -- to replace Gruebel on an interim basis, Reuters reported. Gruebel, appointed in 2009 to rebuild Switzerland\'s flagship bank after a near collapse, said in a message to staff that the trading loss announced last week had shocked him deeply. \"I did not take the step of resigning lightly. I am convinced that it is in the best interests of UBS to approach the future with a new leader at the top,\" he said. Gruebel, a 67-year-old banking veteran who helped turn around rival Credit Suisse last decade, was brought out of retirement to try to revamp UBS after it almost collapsed in 2008 under the weight of more than $50 billion lost on toxic assets. UBS Chairman Kaspar Villiger said the board of directors, who met in Singapore this week, had not lost confidence in Gruebel despite the scandal and had tried to convince him to stay on to allow a more orderly succession next year.