Family of a Pakistani university professor, poet and rights activist who has been critical of the Taliban and also of the government's efforts against militants, has been missing since last week.

Faraz Haider says his brother, Salman Haider, disappeared on Friday. He says Salman's wife got a text message on her phone to go and collect his car from a roadside on Islamabad's outskirts.

No militant group has claimed responsibility so far for the abduction.

Pakistan's ministry of interior on Monday ordered police to step up efforts to find the missing activist.

Local media have reported that a number of other activists like Salman Haider — who run popular social media accounts known for their liberal and leftist views — have also gone missing.