Imran Khan speaks during an event in Lahore. File

Pakistan Prime Minister Imran Khan promised to "investigate" all citizens connected to a massive probe into the hidden wealth of politicians worldwide, after members of his inner circle were implicated in the report.

"If any wrongdoing is established we will take appropriate action," the prime minister said in a series of tweets.

The International Consortium of Investigative Journalists (ICIJ) stated that key members of Imran’s inner circle, including cabinet ministers, their families and major financial backers have secretly owned an array of companies and trusts holding millions of dollars of hidden wealth. The ICIJ said that military leaders have also been implicated but the “documents contain no suggestion that Imran himself owns offshore companies.”

Meanwhile, Pakistan's opposition on Monday called on Imran to order cabinet ministers and aides named in the Pandora Papers to resign from office and face investigation. Major news organisations published the leaked documents on Sunday.

Among those named in the papers are more than 700 Pakistanis, including several members of Imran's cabinet, Pakistani partners of the ICIJ said. Finance Minister Shaukat Tarin, who was among the Pakistanis identified, told Geo TV everyone would be investigated, including himself. He denied wrongdoing.

The so-called "Pandora Papers" investigation — involving some 600 journalists from media including The Washington Post, the BBC and The Guardian — is based on the leak of some 11.9 million documents from 14 financial services companies around the world.

In Pakistan, routinely ranked as among the most corrupt countries in the world, members of Imran's inner circle — including cabinet ministers and their families — are said to secretly own companies and trusts holding millions of dollars.

"We welcome the Pandora Papers exposing the ill-gotten wealth of elites, accumulated through tax evasion & corruption & laundered out to financial 'havens,'" Imran said in a long Twitter thread.

"My govt will investigate all our citizens mentioned in the Pandora Papers & if any wrongdoing is established we will take appropriate action. I call on the international community to treat this grave injustice as similar to the climate change crisis."

Imran, who had run for office on an anti-graft platform, said that global poverty levels were fueled by corruption in tax havens, which he said divert funds away from the general public.

He also slammed wealthy countries for not being "interested in preventing this large-scale plunder nor in repatriating this looted money."

The "Pandora Papers" are the latest in a series of mass ICIJ leaks of financial documents, from LuxLeaks in 2014, to the 2016 Panama Papers, the Paradise Papers in 2017 and FinCen files in 2020.

One of Imran's predecessors, Nawaz Sharif, was ousted by the country's Supreme Court in 2017 over allegations made in the Panama Papers.

A spokeswoman for the main opposition Pakistan Muslim League-Nawaz (PML-N) party of Nawaz Sharif told Reuters Imran had to remove all of those identified in the files.

"Imran Khan is bound to direct all his ministers and aides named in Pandora leaks to resign with immediate effect," Maryam Aurangzeb, the spokeswoman for PML-N, told Reuters.

Sherry Rehman, a leader of the opposition Pakistan People's Party, questioned "shallow" accountability slogans.