If she does manage to rouse large numbers of protesters in the Punjab, this could demonstrate to American officials that General Musharraf has lost popular support in the country.

After arriving in Islamabad from Karachi on Tuesday night, Bhutto met with party stalwarts to organise the protest strategy. On Wednesday morning, she met with members of other opposition parties.

She was expected to meet with the American ambassador to Pakistan, Anne W Patterson, the United States embassy said.

Washington was the main broker for the deal to bring Bhutto back to Pakistan last month after eight years of self-imposed exile abroad where she went to escape prosecution on corruption charges.

The Bush administration, anxious to put a democratic face on the military Government, has been calling in the last few days for General Musharraf to end the emergency rule and call parliamentary elections.

How General Musharraf will respond to the threat of protests, and how far he will listen to the pressure from Washington is one of the key questions in the current stand-off.

In interviews before Bhutto’s announcement, Pakistani analysts said that holding elections would be the easiest way to avoid instability in the country, and that protests led by Bhutto represent the greatest threat to General Musharraf.

At the press conference today, Bhutto was quoted by the BBC as saying: “I appeal to the people of Pakistan to come forward. We are under attack.”

She added that the protest rally could be held in Lahore if the authorities stopped it taking place in Rawalpindi.