The National University of Singapore (NUS) professor who drew criticism last week for referring to lesbianism as "cancers" has been counselled by the university.

In an e-mail to all faculty members, staff and students on Wednesday, NUS provost Tan Eng Chye said he had counselled Associate Professor Syed Muhd Khairudin Aljunied, who acknowledged that his original post "reflected poor judgment in the tone and choice of words".

Prof Tan, who is also NUS deputy president of academic affairs, said Dr Khairudin's comments "contained provocative, inappropriate and offensive language".

This latest controversy, which comes in the midst of a wider debate over whether a Health Promotion Board advisory had normalised same-sex relationships, was sparked by a Facebook post by Dr Khairudin.

In it, the Malay Studies professor had urged scholars, religious teachers and parents to speak up against liberal Islam ideologies and practices such as lesbianism. "All social diseases must end at home, if not, in schools," he said.

He later changed the post to remove the offending words, but it had already attracted the attention of some, including three past and present NUS students. They put up a letter of protest on Facebook on Feb 27, saying what he wrote was "tantamount to hate speech".

In his e-mail, Prof Tan said NUS values the diversity of people, cultures, perspectives and experiences. But the incident is a reminder that issues of race, gender, religion, sexual orientation and value systems "continue to be sensitive, contentious and potentially divisive in Singapore, as in many other societies", he said.

The situation is made worse when views "can be rapidly and widely disseminated via social media to much larger audiences", he said.

Students and staff should thus be mindful and show restraint and respect with their words and actions, especially online, he added.