Thousands of people protested in the Pakistani capital, Islamabad, on Sunday against the execution last month of Islamist Mumtaz Qadri.
Police fired tear gas at protesters who threw stones, damaged property and started fires in the street.
By Monday, thousands were still staging a sit-in around the parliament.
Police bodyguard Qadri murdered his boss, Punjab governor Salman Taseer, in 2011, after Mr Taseer called for reform of Pakistan’s strict blasphemy laws.
Qadri’s supporters say he is a hero and should be considered a martyr.
Critics say the blasphemy laws, which allow the death penalty to be imposed in some cases, are often misused to oppress religious minorities.
The protest was not given much prominence in local media, which is increasingly under official pressure to tone down coverage of events that might encourage unrest.