Shi'a Muslims shout slogans as they protest near the covered bodies (not in picture) of Saturday's bomb attack victims during a sit-in in Quetta on February 18, 2013.

Quetta - Pakistani forces on Tuesday killed four men and arrested seven others accused of killing Shi’a Muslims, including a purported mastermind of a devastating bomb attack that killed 89 people, officials said.

An operation was carried out on the outskirts of the southwestern city of Quetta, where thousands of Shi’as are demanding army protection and refusing to bury the victims of Saturday's bomb attack on their ethnic Hazara community.

The home secretary of Baluchistan province, Akbar Hussain Durrani, and Colonel Maqbool Ahmed from the paramilitary Frontier Corps said the killings and arrests took place during what they called an “ongoing operation”.

“Those who were killed were high-profile targeted killers. They were involved in the killing of a Shi’a judge and senior police officers,” Durrani said.

One of the masterminds of Saturday's bombing in the Quetta suburb of Hazara Town, which killed at least 89 people and wounded more than 200 others, was among those in custody, Durrani added.

Intelligence and paramilitary officers also confiscated bomb-making material, weapons, suicide vests and ammunition during the operation, officials said.

The arrests came just hours before Pakistani cabinet ministers were due to arrive in Quetta in an attempt to negotiate an end to the Shi’a protest.

Thousands of women, men and children have blocked a road in Quetta, refusing to end their sit-in and bury their dead until the authorities take action against the extremists behind Saturday's attack. - AFP