Pakistan has announced three days of mourning for former minorities minister Shahbaz Bhatti.
Mr Bhatti, a Christian, was shot dead in the capital Islamabad on Wednesday.
Christians protested across Pakistan, condemning the killing and denouncing the government. In some places, road blocks were set up and tyres burnt.
The Pakistani Taliban say they killed Mr Bhatti. He had received many death threats for urging reform to Pakistan's controversial blasphemy laws.
Police have issued a sketch of one of the men they believe to be involved in his killing but have so far made no arrests.
In January, Punjab Governor Salman Taseer, who had also opposed the law, was shot dead by one of his bodyguards.
The blasphemy law carries a death sentence for anyone who insults Islam. Critics say it has been used to persecute minority faiths.
Christians demonstrated in Islamabad, Karachi and Lahore. Schools and businesses run by Christians across Pakistan have been closed since Mr Bhatti's murder.
Special services are also being held in churches for the murdered minister.
Christian leaders have dismissed the government's statement that Mr Bhatti's killers will soon be caught.
The BBC's Syed Shoaib Hasan in Karachi says they argue it no longer matters if the killers are caught - what matters is the government's failure to protect minorities.
Mr Bhatti, 42, a leader of the ruling Pakistan People's Party (PPP), had just left his mother's home in a suburb of the capital when several gunmen surrounded his vehicle and riddled it with bullets in daylight, say witnesses.
The minister's driver was spared.
The gunmen, who were wearing shawls, escaped in a white Suzuki car, according to witnesses.
The minister had not been accompanied by his guards or the security escort vehicle that is standard for all Pakistani ministers, and it is not clear why.
Police and federal officials have joined forces to investigate the murder.
The BBC's Ilyas Khan in Islamabad says the joint investigation team has been asked to submit a report to the interior ministry within a week.
Mr Bhatti's funeral will be held in his native village near the city of Lahore on Friday after some close relatives living abroad arrive in Pakistan, our correspondent says.
In January, Mr Bhatti told the BBC he would defy death threats he had received from Islamist militants for his efforts to reform the blasphemy law.
The law has been in the spotlight since a Christian, Asia Bibi, was sentenced to hang in Punjab last November. She denies insulting the Prophet Muhammad.
Christians make up an estimated 1.5% of Pakistan's 185 million population.