A man works near the Pakistan Telecommunication Authority headquarters building in Islamabad. File/AFP

Pakistan's government is throttling the internet and social media while it tests new controls to crush dissent, activists and business leaders say, putting the country's economic recovery at risk.

Since July, internet networks have been up to 40 per cent slower than normal, according to one IT association, while documents, images and voice notes have been disrupted on WhatsApp, used by tens of millions of people.

Digital rights experts believe the state is testing a firewall — a security system that monitors network traffic but can also be used to control online spaces.

"The Internet slowdown is due to the installation of a national firewall and content filtering system by the state aimed at increasing surveillance and at censoring political dissent, especially the criticism of the security establishment for its interference in politics," digital rights expert and activist Usama Khilji told the media.

The authorities appear to be targeting WhatsApp because of its end-to-end encryption capabilities, which enable users to securely share information without it being accessed by any third-party, he added.

The government, which analysts say is backed by the military, and the telecommunications authority, run a by a retired general, for weeks refused to comment on the slowdown.

A logo of the Pakistan Telecommunication Authority is seen on its headquarters building in Islamabad. AFP

It was the defence minister who finally acknowledged what millions of Pakistanis nationwide had already guessed.

"We are undergoing a transition after which all these facilities will be available to you," Khawaja Muhammad Asif told media this week.

"But there will be some controls to prevent threatening and defamatory content against the state and individuals," he added, without confirming whether those controls were part of a firewall.

Prominent Pakistani journalist Hamid Mir has launched a legal challenge against the government over "the apparent installation of a firewall" at Islamabad High Court, which is due to hear the case on Monday.

It comes as Pakistan's military — the country's most powerful institution — says it is battling so-called "digital terrorism".

Regular rallies have been held this year demanding the state do more to tackle militant violence in the border regions with Afghanistan, while protesters in southwestern Balochistan have rallied over alleged rights abuses by authorities in their crackdown on separatist groups.

But analysts say the main target of the digital disruption is the party of jailed opposition leader Imran Khan, still wildly popular and boosted by a young, tech-savvy voter base.

Agence France-Presse