At their last meeting on February 12, Zardari and Sharif, the PML-N chief, had said they would form a coalition government if they emerge as the largest groups in the February 18 polls in order to prevent the military from usurping power from elected representatives.

Sources in the PML-N said the two leaders will also discuss the possibility of organising joint protests in case the polls are rigged. They said the meeting would be crucial as the two parties are expected to perform well in the elections to the national and provincial assemblies.

The latest survey by Gallup Pakistan showed that the PPP is expected to bag 35 per cent of the votes and the PML-N 25 per cent, giving them a clear lead over the ruling PML-Q which is likely to bag 15 per cent of the ballots.

However, observers said the two parties are yet to resolve their differences over several key issues, including the reinstatement of judges who were deposed during 2007's Emergency rule. The PML-N has vowed to reinstate the judges while the PPP has only committed itself to the independence of the judiciary.

Despite allegations of rigging from the opposition, President Pervez Musharraf has vowed to hold free and fair polls. He has also warned that there would be ‘zero tolerance’ for protests during and after the elections and said parties should accept the results thrown up by the polls.