Former President and Co-Chairman of the Pakistan People's Party (PPP) Asif Ali Zardari was arrested on Monday at his residence in Islamabad by a team of the National Accountability Bureau (NAB) for his alleged involvement in a fake bank accounts scam.
His son and PPP chairman Bilawal Bhutto Zardari has appealed to party supporters to remain peaceful.
The case relates to transactions of hundreds of millions of rupees to the two leaders' private companies allegedly through fake bank accounts.
Former Prime Minister Nawaz Sharif is in jail on corruption charges. He denies wrongdoing in this latest "fake accounts" case.
Local media channels said the NAB arrested Mr Zardari following its investigation into false bank accounts and money laundering, with Mr Zardari's sister, Faryal Talpur, also being investigated.
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In recent weeks, the party had accused Prime Minister Imran Khan's government of intentionally targeting political opponents.
Al Jazeera's Kamal Hyder, reporting from Islamabad, said "Zardari has been a controversial figure" in Pakistani politics.
A former businessman and a polo-playing playboy in his younger days, Zardari swept to power in 2008 following a wave of sympathy following the murder of his wife, Benazir, a two-time premier, by Islamist militants in a suicide attack.
BBC correspondent Secunder Kermani says Mr Zardari has always been considered one of the most controversial figures in Pakistani politics.
The anti-graft body has arrested several politicians on corruption charges since Prime Minister Imran Khan took office a year ago.