Professor Theodore G. Hopf's dismissal yesterday marks the third time in recent months that the National University of Singapore (NUS) has taken action against a staff member or former staff member for inappropriate conduct.

In October, Dr Jeremy Fernando, a fellow at Tembusu College who was accused of sexual misconduct, was fired.

NUS said it conducted an internal investigation after it received two complaints alleging that Dr Fernando had "behaved inappropriately as a teaching staff".

Last month, NUS also said it had determined that a former director of the university's East Asian Institute, Professor Zheng Yongnian, had behaved inappropriately with a subordinate by hugging her without her consent during a work meeting.

He would have been given a written warning for his conduct, but as Prof Zheng had left the university in September, NUS recorded the outcome of its internal review in its staff records, the university said.

A raft of sexual harassment allegations involving Prof Zheng had surfaced in August and September on social media, from social media users who identified themselves as NUS staff.

Responding to the statement, Prof Zheng, who spoke through his lawyers, maintained his innocence.

He has said his resignation had nothing to do with the sexual harassment allegations and complaints.