Thousands of Pakistani Christians mourned on Friday as they buried their most prominent government advocate, Shahbaz Bhatti, who was gunned down on Wednesday by Islamic radicals.

 Some 15,000 Pakistanis attended the funeral service, which was held in tight security for fear of more extremist acts.

Shouting slogans like "death for killers," the mourners held mass for Bhatti, a 42-year-old Roman Catholic and the only Christian in the federal cabinet.

In Bhatti's home village of Khuspur, which is mainly populated by Christians, black flags could be seen waving from rooftops.

"The message of Shahbaz Bhatti is to purge Pakistan of killers and hatred," Reverend Father Emmanuel Pervez said during the burial service, according to Reuters. "We will not accept oppression…Bhatti's message is that we should not let Pakistan be defamed."

An avid campaigner for human rights, Bhatti was also a supporter of repealing Pakistan's controversial blasphemy law, which Muslim extremists have used to justify killings.

Leaflets left by al-Qaida and the Taliban at the scene of the shooting accused the Pakistan government of putting Bhatti, an "infidel Christian," in charge of a committee to review the blasphemy law, although the government denies the existence of such a committee.

Along with Bhatti's funeral, Friday marked the beginning of three days of public mourning for the former minister.

A joint statement issued earlier in the week by Catholic and Protestant Churches in Pakistan called the minister "a statesman committed to inter-religious harmony," and said that his killing underlines "the issue of protection for religious minorities, of their life and their freedom."