A fiery Pakistani cleric who has been leading a mass rally outside parliament demanding Prime Minister Nawaz Sharif's resignation says he has "shut the door" on further talks with the government.

Tahir-ul-Qadri emerged from a late night round with government representatives to tell his followers early on Thursday that the talks have failed.

The negotiations were meant to find a peaceful solution to a crisis that has raised fears of political instability in Pakistan.

The cleric, a dual Pakistani-Canadian citizen with a wide following, and Pakistan's cricket-star-turned-politician Imran Khan have been leading mass rallies for two weeks in Islamabad.

They want Sharif to resign over allegations of vote fraud in last year's elections.

Sharif on Thursday cancelled a planned official visit to Turkey to deal with the crisis at home.