ISLAMABAD (AFP) - Pakistan's President on Wednesday intervened to stop authorities from using force against protesters who are calling for parliament to be dissolved in Islamabad's largest political rally in years.

Interior Minister Rehman Malik had warned of a "targeted operation" to disperse an estimated 25,000 demonstrators if they did not go peacefully by Thursday.

"For the safety of the women and children in the protest I request you to leave by tomorrow," Mr Malik told a press conference late on Wednesday, as the rally led by Muslim cleric Tahir-ul Qadri continued for a fourth day.

After the conference, a government statement quoted President Asif Ali Zardari as saying: "There would be no operation against the participants of long march, holding sit-in in the federal capital."

It said Mr Zardari took notice of Mr Malik's statement and directed that "there would be no operation against the marchers and expressed the hope that Dr Tahirul Qadri and his followers would remain peaceful".

Earlier Mr Malik said he was compelled to take action because innocent women and children would be killed because intelligence agencies had reported that suicide bombers may strike Mr Qadri and other protesters.

"There are four credible threats of suicide bombing on Qadri and other protesters and we take it very seriously," Mr Malik said.

"People are falling sick due to cold, rains are about to start and terrorists can strike anytime.

"He should leave tonight." Mr Malik said that a "targeted action" to disperse the protesters could start between any time tonight (Wednesday) or tomorrow night.

"Yes a targeted action is on the cards and it can happen any time because I have to save people from terrorist attacks," said the minister.

"It will not be an operation like Red Mosque," he said, referring to a 2007 week-long military operation in which more than 100 people were killed in Islamabad.

Leading the biggest demonstration in the capital since the current government took office in 2008, Mr Qadri on Wednesday urged mainstream politicians to support his cause.

But the leader of Pakistan's opposition, Mr Nawaz Sharif, announced after consultations with main opposition parties that they would not be joining Mr Qadri in a move that appeared to isolate the populist Canadian-Pakistani cleric.

Mr Qadri's protest rally has threatened to destabilise the nuclear-armed country as it inches towards what would be the first democratic transition of power between two civilian governments at elections due by May this year.

The economy is struggling, Taleban and other violence is at a high, the rupee is sinking, there is an appalling energy crisis and fledgling peace gains with India appear in jeopardy following five deadly cross-border shootings in a week.

Mr Qadri wants parliament dissolved now and a caretaker government set up in consultation with the military and judiciary to implement key reforms such as setting up a new election commission and banning corrupt candidates.

But Mr Sharif has defended the current election commission, saying: "People should refrain from making any demands which are not in the ambit of the constitution."