QUETTA, Pakistan: Protests against attacks on Shi'ites spread across Pakistan on Sunday as the prime minister flew to the western city of Quetta to meet mourners who refused to bury their dead until the government promised them better protection from Sunni militants.

The protests were triggered by twin bombings on Thursday targetting Shi'ite ethnic Hazaras in Quetta, capital of Balochistan province. The attacks, claimed by the Lashkar-e-Jhangvi militant group, killed at least 96 people.

Thousands of Hazaras have been holding vigils at the site of the attacks beside the shrouded victims and were preparing for a third night outside in the cold and rain.

"We want assurances that the killers will be arrested so our younger children will not die also," said Sakina Bibi, 56, who sat alongside the coffins of two of her sons.

"They were my everything," she wept. "Sitting here will not bring them back but it is our right to protest."

Islamic tradition demands that the dead be buried as soon as possible. Leaving the bodies of loved ones above ground for so long is such a potent expression of grief and pain that many people in other cities held protests and vigils in solidarity.

Protests took place in five areas in the commercial capital Karachi, home to 18 million people. Protesters blocked the railway lines and the road connecting the airport to the city. Hundreds also gathered outside the president's private house.

The demonstrations have coincided with another, previously planned, protest due to arrive in the capital Islamabad on Monday. Police have already sealed off portions of the capital in anticipation of the march against government corruption, led by Sufi cleric Muhammad Tahirul Qadri.

Prime Minister Raja Pervez Ashraf Quetta left early on Sunday to address local leaders in Quetta, said presidential aide Naveed Chaudhry. So far, the government has not made any public statement about the attacks.

The Shi'ites want the army to take action against the Lashkar-e-Jhangvi, to guarantee their security and for the provincial government to be fired.

"We will keep protesting until our demands are met," said Raja Nasir Abbas, the secretary general of Majlis-e-Wahdat-ul-Muslimeen, a national organisation of Shi'ite groups and clerics.

Two ministers and three other high-ranking officials wrote to the president and prime minister recommending the chief minister for Balochistan province be fired.

The head of police and the paramilitary Frontier Corps which has primary responsibility for security in the province, should also be replaced, said human rights minister Mustafa Khokhar.

"The government has miserably failed to protect the rights of its citizens," he said.

Sectarian killings have been rising in Pakistan even as deaths from other militant violence have dropped. Human Rights Watch says bombings and gunmen killed more than 400 Shi'ites last year and this year may be even more bloody.

Lashkar-e-Jhangvi, whose roots are in the heartland Punjab province, wants to expel Shi'ites from Pakistan, where they make up about 20 percent of the country's 180 million population.