Police in Pakistan have detained more than 70 people in connection with a recent spate of sectarian violence in southwestern Baluchistan province.

Officials say the arrests were made during a series of raids early Wednesday morning, across the regional capital, Quetta, where Shi'ite Muslims have recently come under increased attacks.

On Tuesday, gunmen attacked a bus carrying Shi'ite Muslims, mostly from the ethnic Hazara community, killing at least 13 people.

Weeks earlier, gunmen attacked a bus bound for Iran, killing 26 Shi'ite Muslim pilgrims also near Quetta. The Sunni militant group Lashkar-e-Jhangvi said it carried out that ambush.

Pakistan has a Sunni Muslim majority, and although most Sunnis and Shi'ites coexist peacefully, extremists often target members of each community.