KARACHI (Reuters) -Pakistan is spying on millions of its citizens using a phone-tapping system and a Chinese-built internet firewall that censors social media, in one of the most comprehensive examples of state surveillance outside China, Amnesty International said.

The rights watchdog said in a report released on Tuesday that Pakistan's growing monitoring network was built using both Chinese and Western technology and powered a sweeping crackdown on dissent and free speech.

Already restricted political and media freedoms in Pakistan have tightened in recent years, particularly after the military broke with then-Prime Minister Imran Khan in 2022, who was later jailed and thousands of his party activists were detained.

Pakistan's spy agencies can monitor at least 4 million mobile phones at a time through its Lawful Intercept Management System (LIMS), while a firewall known as WMS 2.0 that inspects internet traffic can block 2 million active sessions at a time, Amnesty said. 

The two monitoring systems function in tandem: one lets intelligence agencies tap calls and texts while the other slows or blocks websites and social media across the country, it said. 

The number of phones under surveillance could be higher as all four major mobile operators have been ordered to connect to LIMS, Amnesty technologist Jurre van Berge told Reuters.

"Mass surveillance creates a chilling effect in society, whereby people are deterred from exercising their rights, both online and offline," the report said.

Amnesty said its findings draw on a 2024 Islamabad High Court case filed by Bushra Bibi, the wife of former premier Khan, after her private calls were leaked online. 

In court, Pakistan's defence ministries and intelligence agencies denied running or even having the capacity for phone tapping. But under questioning, the telecom regulator acknowledged it had already ordered phone companies to install LIMS for use by "designated agencies." 

Pakistan's technology, interior, and information ministries, as well as the telecom regulator, did not respond to questions from Reuters about the Amnesty report.

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Pakistan is currently blocking about 650,000 web links and restricting platforms such as YouTube, Facebook and X, Amnesty said. 

The controls have hit hardest in the insurgency-hit Balochistan province, where districts have faced years-long internet blackouts, and rights groups accuse the military of disappearances and killings of Baloch and Pashtun activists, charges it denies.

Amnesty said it also reviewed licensing agreements, trade data, leaked technical files and Chinese records tying the firewall supplier to state-owned firms in Beijing.

It added that the firewall is supplied by the Chinese company Geedge Networks. The company did not respond to a request for comment. 

Monitoring centres for mobile calls are common globally but internet filtering for the public is rare, said Ben Wagner, Professor of Human Rights and Technology at Austrian university IT:U. 

Having both in Pakistan "constitutes a troubling development from a human rights perspective" and "suggests greater restrictions on freedom of expression and privacy will become more common as such tools become easier to implement," he said.

Amnesty said the firewall uses equipment from U.S.-based Niagara Networks, software from Thales DIS, a unit of France's Thales, and servers from a Chinese state IT firm. An earlier version relied on Canada's Sandvine. 

Niagara told Reuters it follows U.S. export rules, does not know end users or how its products are used, and only sells tapping and aggregation gear. 

Amnesty said the phone tapping system was made by Germany's Utimaco and deployed through monitoring centres run by UAE-based Datafusion.

Datafusion told Amnesty that its centres are only sold to law enforcement and that it does not make LIMS, while AppLogic Networks, the successor to Sandvine, said it has grievance mechanisms to prevent misuse.

The other companies named in the report did not respond to requests for comment.