The government agreed Monday to restore deposed judges. Activists want further reforms.
Opposition leader Nawaz Sharif defied house arrest to rally protesters in Lahore Sunday.
The opposition lawyer has championed the popular protest that began Thursday. Some see a rule-of-law hero; others cite political expedience.
Authorities arrested hundreds of lawyers and activists and banned public gatherings in two provinces.
Media reports suggest that the Pakistani investigation has centered on the same group accused of carrying out the Mumbai attacks.
Protesters rallied in several cities after a court banned popular opposition leader Nawaz Sharif from running for office.
Gunmen abducted John Solecki, head of the UN refugee agency in Quetta, on his way to work Monday.
It summoned the US ambassador Thursday to formally complain after an attack hit deep inside Pakistani territory.
Pakistan asked the IMF for a loan Wednesday, after allies rebuffed its requests for aid.