ISLAMABAD (Reuters) - Former Pakistani prime minister Nawaz Sharif was sentenced to seven years in prison on Monday and fined $25 million on corruption charges that he says were politically motivated.

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The anti-corruption court in Islamabad said in its ruling that the three-time prime minister was unable to prove the source of income that had led to his ownership of a steel mill in Saudi Arabia. Under Pakistani law, this is taken to prove corruption.

Sharif had already been sentenced by the same court to 10 years in prison on charges related to the purchase of upscale apartments in London, after the Supreme Court removed him from power. He was freed from custody in September pending an appeal.

Sharif’s supporters said he would also appeal against his latest conviction.

“Appeal is our right, we will protest but will remain peaceful,” former prime minister Shahid Khaqan Abbasi, who had succeeded Sharif last year, told reporters outside the courthouse.

Sharif was ousted and disqualified from holding office by the Supreme Court in July 2017, and convicted in absentia a year later. He was arrested on July 13 on returning from London.

The court ruled on Thursday on two charges related to Sharif’s assets: the Al-Azizia Steel Mills in Saudi Arabia, set up by Sharif’s father in 2001, and Flagship Investments, a company established by his son, Hasan Nawaz, that owns luxury properties in Britain.

Sharif was found to have been unable to demonstrate that his family had acquired the steel mill legitimately, but was acquitted on the second charge, relating to Flagship.

Sharif denied the charges which he said were politically motivated. He accused the military and courts of working together to end his political career and destabilize his Pakistan Muslim League-Nawaz (PML-N) party.

Sharif was once a favorite of Pakistan’s powerful generals but fell out with them. The military has denied exerting any influence over the court proceedings.

Daniyal Aziz, a former lawmaker from Sharif’s party, criticized the National Accountability Bureau, the watchdog that charged Sharif, and described the verdict as “the weaponization of anti-corruption”.

“With each passing day an expression of a double standard is coming forward from the NAB,” Aziz said.

Before the verdict, hundreds of Sharif supporters threw stones outside the courthouse at police, who fired teargas.

Five months ago, Sharif’s PML-N lost a general election to the party of Imran Khan, the new prime minister whose anti-corruption campaign and street protests spurred the cases against Sharif.

PML-N and other opposition politicians allege the election was rigged to favor Khan, who is seen as close to the army.

Both Khan and the military have denied colluding against Sharif and the PML-N.