Interior Minister Chaudhry Nisar on Thursday threatened to block "all social media websites" that host blasphemous content hours after the Islamabad High Court (IHC) ordered the government to open an investigation into online blasphemy.

The issue came to the fore in January, when five activists were reported missing. Four of the missing activists were returned to their families weeks later, but not before they were tarnished by a virulent campaign to paint them as 'enemies of Islam'.

On Thursday, the IHC ordered the government to open an investigation into online "blasphemy", threatening to ban social media networks if they failed to censor content deemed insulting to Islam.

"We will go to any extent [including] permanently blocking all such social media websites if they refuse to cooperate," the minister said in a statement.

No country can allow religious sentiments to be hurt or top state functionaries to be subjected to ridicule under what the minister described as "the pretext of freedom of expression."

IHC judge Justice Shaukat Aziz Siddiqui asked the government to form an investigative committee to report back next Monday over the issue, saying he could order social media sites to be blocked if offending content remained online.

"The judge ordered the government to make a Joint Investigation Team with Muslim officials only to look into the blasphemy issue," said advocate Tariq Asad, the petitioner in the case.

Rights groups say the label of 'blasphemer' is liberally applied by religious conservatives in order to silence criticism of extremism.

Even unproven allegations can be fatal. At least 65 people, including lawyers, judges and activists, have been murdered by vigilantes over blasphemy allegations since 1990, according to a recent think tank report.

Pakistan previously banned Facebook for hosting blasphemous content for two weeks in 2010, while YouTube was unavailable from 2012 to 2016 over an amateur film about Prophet Muhammad (Peace Be Upon Him) that led to global riots.

But Pakistan later came to agreements with major internet firms to block within the country material that violated its laws, generally once the companies had performed their own cross-checks.

Yasser Latif Hamdani, a lawyer who worked to get YouTube unblocked, said previous web censorship had also originated with court orders and the judge could succeed in implementing a fresh set of bans.