TOKYO (REUTERS) - Nissan Motor said Carlos Ghosn, who has led the Japanese automaker for the past 16 years, will step aside as chief executive officer, handing over the helm to a long-time company veteran.

The announcement ends years of speculation over when Ghosn would relinquish the top job at Nissan to focus on French alliance partner Renault, whose investors have grumbled that he was stretched too thin leading two major automakers.

Ghosn, who added a third chairmanship at Mitsubishi Motors Corp in December, will remain as chairman of the board at Nissan. Hiroto Saikawa, currently co-CEO, will be the sole chief executive officer from April 1.

"Having recently taken on new responsibilities at Mitsubishi Motors ... I have decided that the time is right for Hiroto Saikawa to succeed me as Nissan's CEO," Ghosn said in a statement.

"As Nissan's chairman, I will continue to supervise and guide the company, both independently and within the Renault-Nissan-Mitsubishi Alliance," he said, adding the move would allow him to devote more time to running the alliance.

Saikawa, a 40-year Nissan veteran, has served as co-CEO since last November after the automaker took a controlling stake in Mitsubishi Motors. Prior to that, he served as chief competitive officer, and also currently heads Japan's auto industry lobby.