Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

ISLAMABAD — Four Pakistani activists who have been critical of the country's government have disappeared in as many days, according to family members and colleagues.

The men vanished three different places — Islamabad, Lahore and Morkhanda — alarming friends who do not know what has become of them.

The Morning Rundown Get a head start on the morning's top stories. This site is protected by recaptcha

Pakistan’s security and intelligence agencies have a decades-old reputation of harassing journalists, writers and academics. But no one with whom NBC News spoke alleged publicly that the government was responsible for the disappearances.

The missing men are: Salman Haider, 36, a lecturer at Fatima Jinnah University; Waqas Ahmad Goraya and Asim Saeed who, along with Haider, curated liberal posts, primarily on Facebook; and an activist named Ahmad Naseer Raza, who was said to be the voice behind the anti-conservative @bhensaa Twitter account. The account was removed from Twitter over the weekend.

Haider, 36, disappeared Friday night from the Islamabad suburb of Bani Gala, according to his brother Zeeshan Haider. Salman Haider went out with friends that evening and never came home, his brother added.

He was known for writing left-leaning poetry and for criticizing what he alleged was the government’s failure to protect minorities.

Haider's wife received a text message from her husband's phone asking her to collect his car from a highway, his brother said. No one has heard from Haider since. But his brother said authorities have promised that he will be located soon.

Sarafaz Hussain, a spokesman for Pakistan's Interior Ministry, said the government was “going to do everything it can to locate Mr. Haider.”

Hussain said he was aware of the other disappearances, but he did not comment on them.