ISLAMABAD -  Opposition lawmakers on Monday called for an investigation into the disappearance of four social activists last week, including a prominent university professor who often spoke out over disappearances of fellow campaigners.

Five Pakistan People's Party (PPP) lawmakers asked for a swift government response in parliament and raised concerns about the disappearance of poet and rights activist Salman Haider, as well as three others.

The lawmakers submitted a call-attention notice in the National Assembly secretariat, asking the interior minister to brief the house in the upcoming session about the disappearance of academic and social activist Salman Haider.

Haider, a human rights activist and a professor of the Fatima Jinnah Women University, went missing from the Bani Gala area of Islamabad a few days back and later his car was recovered by police from the Koral Chowk area. Since then, his whereabouts have not been known. The police claimed to have found some clues, however, no headway has been so far made to trace him, putting a question mark on the authenticity of the police claim.

PPP lawmakers — Dr Nafisa Shah, Syed Naveed Qamar, Dr Azra Fazal, Shazia Mari and Ms Shahida Rehmani — have submitted the calling attention under Rules of Procedure and Conduct of Business of National Assembly, 2007.

“We, the undersigned, would like to invite the attention of the minister for interior towards the disappearance of the poet, social activist and academic Salman Haider, causing grave concern among the public,” the call-attention notice reads.

The lawmakers said Haider has been missing since Friday but law enforcing agencies have not been able to trace him or provide a satisfactory answer about the serious incident.

They also said that it was highly alarming that activists and intellectuals from other parts of the country have also gone missing in the last one week. “The pattern of these disappearances suggests that it is a planned and a coordinated action taken to silence voices which are critical of the prevalent socio-political issues in Pakistan,” they said, without implicating anyone directly.

Rights activists say the disappearances have stirred unease among those critical of the government and Pakistan's powerful military, though no evidence has been provided to suggest state actors were involved.

It is not clear how the four men disappeared and Sarfraz Ahmed, Interior Ministry spokesman, said in a text message that "everything is being done to recover Salman". Ahmed did not respond to requests for comment about the other activists, or the PPP notice served in the lower house of parliament.

Haider and teaches at Fatima Jinnah Women's University in Rawalpindi disappeared on January 6 in the capital.

Last year, Haider wrote a poem about human rights abuses in Pakistan's restive Baluchistan province, including a line about his friends' friends disappearing. He queried whether his friends, or even he himself, will be next to suffer such a fate.

"It's ironic that the thing he was talking about six months ago happened to him," said Haider's brother Zeeshan. "(If) in the capital of Pakistan, a professor who has a very active social media presence can disappear, what will happen to an average person who does not have anyone behind him?" Zeeshan added.

Two of the missing activists, Waqas Goraya and Aasim Saeed, live in the Netherlands and Singapore. Their relatives said they were taken on Jan. 4 while visiting Pakistan. The fourth activist, Ahmed Raza Naseer, suffers from polio.

"The status 'missing' is causing a lot of fear in larger social media circles," says Shahzad Ahmed, director of cyber security think tank Bytes for All. "This is going to cause huge self-censorship in the media."

Meanwhile, civil society activists will launch nationwide protests from today (Tuesday) against missing of social media activists.

Progressive political parties and organisations will be holding protest demonstrations in cities across the country to demand the recovery of social media activists Salman Haider, Waqas Goraya, Aasim Saeed, and others who have disappeared over the last few days, said Fahad Deshmukh, a human rights activist.

He said young activists from Islamabad and adjoining areas will gather at Islamabad Press Club at 4pm today. He demanded the state authorities to immediately locate and recover the missing activists, bloggers, and journalists. He also asked the authorities to secure the constitutional and democratic right to freedom of expression as well as rule of law in Pakistan.

According to activists, a protest was held in Karachi on Monday while demonstrations in Lahore and Peshawar will be held in the coming days.