Jawad Louay al-Yasseri, whose father was then governor of the central province of Najaf, was arrested in 2018 and sentenced to life in prison, which amounts to a 20-year term in Iraq.

On January 10, he and two fellow convicts in the same case were quietly granted a presidential pardon and released, a senior police official told AFP.

The decision caused a stir among MPs and journalists who have criticised an alleged behind-the-scenes deal involving the governor, who resigned a day before the pardon was requested by the prime minister.

"Thousands of victims of confessions under torture are rotting in prison without His Excellency the President thinking of pardoning them," Mashan al-Jabouri, a member of the main Sunni bloc in parliament, tweeted.

The ex-Najaf governor, who stepped down in the face of corruption accusations against him, has insisted on his son's innocence and said he was targeted to damage his father.

Hadi al-Salami, a deputy for the Shiite holy city of Najaf, capital of the province of the same name, wrote an open letter on Sunday to Saleh and Prime Minister Mustafa al-Kadhemi to demand an explanation.

Saleh has ordered an "urgent investigation" and to correct any judicial "vice", in a statement issued by his office.

It said the pardon had been based on a "recommendation" from the government.

In 2019, Iraq was rocked by massive protests fuelled by charges of widespread official corruption, incompetence and withering economic hardships.