Pakistan's fugitive former oil and gas chief has been arrested in Abu Dhabi on suspicion of embezzling $850 million in a scandal that could spark a criminal case against the prime minister, an official said Wednesday.

Tauqir Sadiq was arrested a week after Pakistan's top court ordered a case to be registered against Prime Minister Raja Pervez Ashraf over the matter, raising pressure on the government as it nears the end of its five-year term in office.

Sadiq is accused of taking $850 million in kickbacks and commissions while head of Pakistan's oil and gas regulatory authority between 2009 and 2011, at a time when Ashraf was water and power minister. Sadiq fled Pakistan last year.

The scandal is the latest standoff between Pakistan's judiciary and the civilian government, which have been at loggerheads for years.

"We can confirm his arrest. He has been detained in Abu Dhabi," said Zafar Iqbal, spokesman for Pakistan's anti-corruption National Accountability Bureau (NAB), which has been investigating the graft allegations.

Iqbal said that Sadiq could return to Pakistan "in the next few days" and "as soon as the legal formalities are complete".

On January 24, the court ordered a case to be registered against Ashraf, Interior Minister Rehman Malik and another member of the main ruling Pakistan People's Party over Sadiq's appointment in 2009 and absconding in 2012.

It is one of two corruption cases being heard by the Supreme Court dating back to Ashraf's tenure as water and power minister. Pakistan's top judge ordered Ashraf's arrest in the other case on January 15.

On Wednesday, the court also summoned NAB chairman Fasih Bokhari to appear Thursday over a letter he sent to President Asif Ali Zardari threatening to resign.

Chief Justice Iftikhar Muhammad Chaudhry said the document, which has been made public, amounts to "criticising and pressurising" the court.

In the letter, Bokhari accused the court of interfering in NAB investigations, particularly against politicians, and endangering the independence of their work.

Members of the government accuse judges of waging a politically motivated witch hunt against the administration, which in March 2013 will become the first elected civilian government in Pakistan to complete a full term in office.

In June last year, the Supreme Court sacked Ashraf's predecessor over his refusal to ask Switzerland to reopen corruption cases against President Asif Ali Zardari.