Konrad Hummler, one of Switzerland's most high-profile bankers, said on Thursday he needed to focus on the U.S. case against Wegelin on charges it enabled Americans to evade taxes on at least $1.2 billion in offshore bank accounts.

"The legal dispute in the tax row between the United States and Switzerland demand the engagement of all my physical and intellectual capacities," he said.

Hummler said he was handing chairmanship of the NZZ to Franz Steinegger for the time being, adding that his position as a member of the newspaper's board, to which he was elected in 2011 for a period of four years, was unaffected.

Hummler had come under pressure to step down as NZZ chairman for fear the Wegelin case could damage the reputation of Switzerland's oldest newspaper -- the voice of the country's business establishment.

Unusually outspoken among Swiss bankers who typically prefer work in relative obscurity, Hummler courted press attention, which he successfully translated into business for Wegelin.

However, his outspoken style also helped anger U.S. authorities, especially after he wrote a "Farewell, America" letter to clients in 2009, taken by many rivals as a codified invitation for tax evaders to bring funds to Wegelin.

Wegelin broke itself up last month in the face of the U.S. investigation, moving most of its clients and assets of 21 billion Swiss francs ($23 billion), to Notenstein Privatbank, in turn bought by Swiss cooperative bank Raiffeisen for an undisclosed sum.

Switzerland has been lobbying for a year to get investigations against 11 banks, including Credit Suisse and Julius Baer, dropped in return for the payment of hefty fines and the transfer of client names.

($1 = 0.9128 Swiss franc)

(Reporting by Emma Thomasson; Editing by Dan Lalor)

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