Pakistani security forces on Tuesday killed four suspects linked to last weekend's massacre of about 90 Shi'ite Muslims in the western city of Quetta, authorities told Efe.

The police operation was launched Monday night on the direct order of Prime Minister Raja Pervaiz Ashraf and authorities also arrested "several suspects who were armed," one source said.

The ongoing operation is aimed at "eliminating those responsible for playing with the lives of innocent civilians and restoring peace and security in Quetta," Ashraf's office said in a statement.

The Saturday attack was very similar to another with a similar death toll a little more than a month ago and responsibility for both was claimed by the radical sectarian group Lashkar-e Jhangvi.

The latest massacre has further inflamed Pakistan's already enraged Shi'ites - who number roughly 40 million nationwide - and since Sunday protests have been intensifying in Quetta and other major cities.

Qadir Ali, a spokesman for the mainly Shi'ite Hazara Democratic Party, told Efe that the police operation under way "is not enough" and that only bringing in the army to take control of Quetta's security will calm the protests.

Since Monday, about 10,000 Shi'ites, among them relatives of the massacre victims, have been out on the streets of Quetta, and they are refusing to bury their loved ones' remains until the military takes charge of the situation. EFE