The official said that Makhdoom Shahabuddin, the outgoing textile minister, was the likely candidate, as did another member of the ruling PPP. They didn't give their names because they weren't authorized to speak on the record about internal party decisions.

Shahabuddin is from Rahim Yar Khan, a conservative Islamic city in south of Punjab province. He is considered a party loyalist and was known to be close to Zardari's late wife Benazir Bhutto, who headed the party but was killed in 2007 by Islamist militants.

Whoever takes over will not have long in power and is likely to face a rocky ride.

The government must call elections before March next year. Under the constitution, polls can only be held under a caretaker government, which must be in place three months before election day. Many analysts have speculated that the current political upheaval may expedite the polls, possibly to November. Elections before that date are considered unlikely because of the fierce summer heat.