The investigators are probing whether the Prime Minister has purchased four expensive flats in London through an offshore company.

A joint investigation team (JIT), comprising financial experts and representatives of military intelligence agencies, grilled Pakistani Prime Minister Nawaz Sharif for three hours on Thursday in connection with the Panama papers probe into his family’s assets. The JIT, constituted by the Supreme Court, has already questioned the Prime Minister’s two sons. His brother and son-in-law will appear before the panel on June 17 and 24.

Mr. Sharif told reporters after the interrogation that no one had proved any charges on him. In an apparent bid to challenge the military establishment, the Prime Minister said the days of puppet regimes are over.

The investigators are probing allegations that Mr. Sharif’s family bought four expensive flats in London through an offshore company using unaccounted money. Mr. Sharif had told Parliament last year that his late father set up steel mills in the Gulf and the proceeds from selling those mills were used to purchase the flats.

In his defence in the Supreme Court, Mr. Sharif’s counsel presented a letter from a Qatari prince who testified that the flats were purchased by his company which were later sold to the Prime Minister’s son. Last year, Panama papers revealed names of people and families who have hidden money from authorities and purchased assets outside their countries, including Mr. Sharif’s family members.

The JIT has been given two months by the Supreme Court to complete the probe of which 40 days have already passed.

Mr. Sharif's government has accused some of the JIT members of having sympathies for the opposition parties. The Supreme Court had rejected the objections and asked the JIT to continue its work.

The case was first highlighted in 1996 by a U.K. newspaper, which alleged that Mr. Sharif laundered money to buy the apartments in London’s expensive Park Lane area. A case was registered against him but was shelved when he came back to power in 1997.

“Details of my assets are already available with all relevant institutions, including the Supreme Court. Today, I submitted them to the JIT as well. I have been the Prime Minister for the third time. But not a single allegation of financial corruption could be brought against me. Yet, I have put myself and my family up for trial and provided the details of financial transactions made even before my own birth,” Mr. Sharif said about the case. Opposition leader Imran Khan has criticised Mr. Sharif's remarks after appearing before the JIT. “Since he (PM) has not anything concrete to say before the JIT, he has chosen to point fingers towards two institutions, army and judiciary by terming the case as a conspiracy,” Mr. Khan said in a statement.