UBS AG said Tuesday that Yasuki Matsui will resign as chairman of the investment banking division in Japan, becoming at least the third senior executive in the country to leave a European bank since October.

Matsui, 55, who joined Switzerland's biggest bank in 2007 from Morgan Stanley as cohead of Japan investment banking, will leave on Dec. 31, Eiko Noda, a Tokyo-based spokeswoman, said. She declined to comment on why he is leaving and whether the Zurich-based bank will replace him.

UBS, which took a $2.3 billion loss from unauthorized trading in September, is cutting jobs as it shrinks the investment bank to concentrate on wealth management. Credit Suisse Group AG, its biggest domestic rival, is also eliminating jobs and trimming riskier assets amid stricter banking rules and global market turmoil stemming from the debt crisis in Europe.

Taiji Okusu, head of investment banking for Credit Suisse in Japan, left the firm last month. Credit Suisse's Japan chief executive officer, Paul Kuo, will step down Jan. 1.

Tomonori Ito, a managing director at UBS who had been cohead of investment banking in Japan, resigned earlier this year to become a professor at Tokyo's Hitotsubashi University.

UBS plans to cut risk-weighted assets at the investment bank by 145 billion Swiss francs ($158 billion), or almost half, by 2016 under new banking rules developed by global finance regulators in Basel, Switzerland. The investment bank will aim for a head count of about 16,000 in the future, Chief Executive Officer Sergio Ermotti said last week, from 17,878 at the end of September.