Dr Riaz Ahmed, a political activist and chairman of department of Applied Chemistry at the University of Karachi (KU), has gone missing from Karachi, his family said on Saturday.
Dr Ahmed last contacted his wife last night from the university at around 8pm and has not been in contact since 9pm Friday night, his family said.
His phone has been switched off.
A KU spokesperson said that the university has been informed about the associate professor's disappearance and is attempting to locate him.
Activists associated with the Pashtun Tahaffuz Movement (PTM) have connected the incident to an alleged crackdown on sympathisers ahead of a rally scheduled for tomorrow.
They have demanded the release of Dr Ahmed and several others allegedly detained as part of the same crackdown.
Describing the professor as Karachi's "agitator-in-chief", acclaimed author and writer Mohammad Hanif has also demanded that he be released.
Meanwhile, lawyer and activist Jibran Nasir has said that Hashim Khan, who played an instrumental role in highlighting Naqeebullah Mehsud's extrajudicial killing, was picked up last night for supporting PTM.
Dr Ahmed had been arrested last year by the Sindh Rangers on charges of possessing a pistol, which he maintains were false and fabricated.
He was picked up minutes before he was to hold a press conference at the Karachi Press Club to demand proper treatment for now deceased Muttahida Qaumi Movement-London leader and professor Dr Hassan Zafar Arif, who had been in police custody at that time.
Ahmed was released on bail days later.
The associate professor was also the core organiser of a seminar on Balochistan's missing persons held at KU in 2015 after a similar session was cancelled by the Lahore University of Management Sciences.
KUTS condemns "mysterious" disappearance
Karachi University Teacher's Society (KUTS), in an emergency session, strongly condemned the “mysterious” disappearance of Dr Ahmed.
It expressed extreme grief and anger over the fact that "a teacher who provides wisdom and enlightenment to the society is made to mysteriously disappear, resulting in a highly negative societal impact".
The teachers' society expressed grave concerns over the atmosphere of fear and suffocation that was being felt at the university.
The attendants of the meeting also expressed concern over the fact that such incidents were being experienced in their varsity in quick succession, not only disturbing the instructional and analytical environment but also creating a situation where people were feeling disheartened.
KUTS said it has reached out to the chief of army staff, chief justice of Pakistan, prime minister and Sindh chief minister, demanding the expedient recovery of Dr Ahmed.
In the wider interest of students, however, the KUTS decided to go ahead with the PhD and MPhil entry tests scheduled for May 13 but warned that the "entry test copies will not be checked and the results will not be announced” until Dr Ahmed’s recovery.
The KUTS further said that it will hold a protest in the university's arts lobby after the exams on Sunday.