An international human rights watchdog has urged Pakistani authorities to observe a recent ruling from the country's Supreme Court and stop using the country's anti-corruption agency as a tool to detain government critics.

Human Rights Watch (HRW) said in an August 6 report that Pakistani authorities should investigate and prosecute officials from the National Accountability Bureau (NAB) who are responsible for unlawful arrests and other abuses.

The NAB was established in 1999 as an ostensibly independent anti-corruption body during the military rule of General Pervez Musharraf.

Musharraf gave the NAB unchecked powers of arrest, investigation, and prosecution -- allowing it to detain people for up to 90 days without charge.

Pakistan's Supreme Court ruled on July 20 that the NAB had infringed upon the right to fair trial and due process in cases against two opposition politicians: Khawaja Saad Rafique and Khawaja Salman Rafique.

The two had been arrested by the NAB and held in detention for 15 months without reasonable grounds, the Supreme Court ruled.

The court granted the men bail and criticized the NAB for showing "utter disregard for the law, fair play, equity, and propriety," ruling that the "case was a classic example of trampling on fundamental rights [and] unlawful deprivation of freedom," the New York-based rights watchdog said.

"The Pakistani Supreme Court judgment is just the latest indictment of the NAB's unlawful behavior," HRW Asia Director Brad Adams said. "Pakistani authorities should stop using a dictatorship-era body, possessing draconian and arbitrary powers, to intimidate and harass opponents."

HRW also urged Pakistani lawmakers to carry out urgent reforms in order to ensure the anti-corruption agency has real independence.

The Supreme Court ruling also had raised concerns about the use of the NAB as a tool against government opponents.

It cited a report issued in February by the European Commission that criticized the NAB for bias, saying "very few cases of the ruling party ministers and politicians have been pursued since the 2018 elections, which is considered to be a reflection of the NAB's partiality."

The HRW report also criticized the NAB's 'arbitrary use of powers of arrest.'

It mentioned the case of Mir Shakil-ur-Rehman, editor in chief of Pakistan's largest media organization, Jang Group.

Shakil-ur-Rehman was arrested in Lahore by the NAB on March 12 on charges related to a 34-year-old property transaction.

HRW says he has remained in the agency's custody ever since.

An arrest "has to be justified.... The power of arrest should not be deployed as a tool of oppression and harassment," HRW said, quoting the Supreme Court ruling.

In another example of harassment, HRW said the NAB had summoned the former president and opposition leader, Asif Ali Zardari, to appear in person to record a statement -- denying his request to record his statement through a video link because of his ill health and the COVID-19 pandemic.

Zardari previously spent 11 years in prison -- more than half of that time in NAB custody -- without being convicted of a crime, HRW said.

"Pakistani authorities should uphold the government's human rights obligations," Adams said. "Pakistan's parliament should amend or repeal the NAB ordinance to ensure that the principles of fair trial, due process, and transparency are not compromised on the pretext of accountability."

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