The battle for control of Arm Ltd.’s China business is escalating with new lawsuits aimed at keeping the unit’s controversial chief executive in power, further complicating SoftBank Group Corp.’s efforts to sell the business to Nvidia Corp.

The dispute erupted almost a year ago in June after the board voted to oust Arm China Chief Executive Officer Allen Wu for conflicts of interest, but he refused to leave. Now the Chinese unit, which remains under Wu’s control, has filed lawsuits against three senior executives the board designated to replace him, according to people familiar with the matter. The previously unreported suits could take years to resolve, suggesting Wu may remain entrenched.

Wu fired the three men — including co-CEO Phil Tang — but they were subsequently reinstated by the board. In the new lawsuits, Arm China is suing the trio, demanding they return company property, according to the people.