Pakistan's former interior minister and ally of ousted leader Iman Khan was arrested on Thursday, a few hours after another senior opposition figure was released from custody.

Sheikh Rashid Ahmed, who heads a party that was in a coalition with Khan, appeared at Islamabad court where he was remanded in custody for two days.

Ahmed was arrested in connection with remarks he allegedly made against former president Asif Ali Zardari, accusing him of hatching a "murder plot to eliminate Pakistan Tehreek-e-Insaf (PTI) chief Imran Khan", according to a police charge sheet.

"He tried to incite people," said Raja Inayat ur Rehman, an official with Pakistan Peoples Party which filed the complaint and of which Zardari is co-chairman.

Pakistan is facing overlapping security, economic and political crises, with the weak coalition government battling plummeting popularity ahead of a general election due in October.

The arrest shortly after midnight on Thursday came just hours after Fawad Chaudhry, who was information minister under Khan, was bailed by an Islamabad court after spending a week in detention.

Chaudhry was arrested on suspicion of having "harassed and intimidated" election commission officials and their families in televised comments, according to a police report shared by Khan's PTI party.

Khan and other leaders of his party have been caught up in a slew of court cases, a common hurdle facing opposition groups, which rights monitors say are orchestrated to shut them out of office.

Former cricket star Khan was ousted by a vote of no-confidence in March last year after some of his coalition partners switched allegiance.

He has since pushed for early polls by holding rallies, pulling out of parliament and dissolving the two provincial assemblies his party controls in a bid to force the government's hand.

Since then, the new government has overseen a further backslide in the economy, holding off for months on meeting tough International Monetary Fund (IMF) conditions that would help bring some stability, as its popularity waned.

But with the prospect of national bankruptcy looming and no friendly countries willing to offer less painful bailouts, Islamabad has started to bow to pressure prompting an urgent visit by the IMF this week.