An anti-graft tribunal sentenced former Prime Minister Nawaz Sharif to seven years in prison for corruption on Monday, drawing criticism from his party, which said the decision was a "black stain" on the justice system.

The verdict came after Sharif was removed from power last year over corruption allegations. Sharif, who was serving his third stint as prime minister, has denied any wrongdoing.

He is accused of possessing assets beyond his known sources of income, and was arrested after the ruling was announced.

He can appeal the verdict, under which he was also fined $25 million for not disclosing how his family set up the Al-Azizia Steel Mills when he was exiled to Saudi Arabia by Pervez Musharraf, a former dictator who toppled Sharif's government in 1999.

The same court acquitted Sharif in a second case relating to his family's business in Britain.

According to Pakistan's anti-graft body, it will challenge the acquittal of Sharif, who was sent to jail a day before his birthday.

After being held at a jail in the garrison city of Rawalpindi, Sharif, on his request, is expected to be taken to a jail in Lahore on Tuesday.

"They had to punish him and they have punished him in a false case," said Shahid Khaqan Abbasi, a top leader of Sharif's Pakistan Muslim League party, who served as prime minister when Sharif was removed from power last year.

"People will not accept this verdict," he said.

Abbasi said Sharif was being victimized for political reasons.

Hours after the verdict, Information Minister Fawad Chaudhry said the court decision "unmasked the real face of Sharif who failed to provide money trail of his assets."

Those defending Sharif should be ashamed, he said, as the Pakistani people have been defrauded.

Monday's conviction and sentencing was the latest blow to Sharif who was sentenced to 10 years in prison in July over the purchase of luxury apartments in London. He appealed that sentence and was released on bail in September, along with his daughter and her husband, who were co-accused in the case stemming from documents leaked from a Panama law firm.

The two cases on which the court ruled Monday were related to Sharif's foreign assets, which he insists are owned by his sons.

His two sons, who are currently living in London, were declared absconders by the court.

Shortly before the announcement of the verdict, clashes erupted between supporters of Sharif and police in Islamabad. Several female supporters of Sharif were seen crying and chanting slogans.

Sharif's daughter, Maryam Nawaz, has suggested he is being punished for resisting "unseen forces," an apparent reference to the military, which has directly ruled Pakistan for half its modern history and retains a powerful role behind the scenes.

She wrote in a series of tweets Monday that the people of Pakistan were standing by her father.

"For how many times will you target one man? For how many times will you punish him," she posted.