At least three paramilitary guards were killed Sunday when a suicide bomber on a motorbike blew himself up in Quetta, southwestern Pakistan, police said.

The bomber targeted Frontier Constabulary guards in the Mian Ghundi neighbourhood of the city close to the Afghanistan border where Hazara Shiite merchants were trading vegetables.

Azhar Akram, a deputy inspector general of police, told AFP that 20 people were injured in the blast, including civilians.

A spokesman for the police's Counter-Terrorism Department confirmed the toll.

Shiite Muslims have been frequently targeted in restive Balochistan by radical Sunni Islamist groups, who consider them a heretical sect.

Frontier guards have also been targeted by Baloch insurgents, who have been waging a simmering insurgency for greater autonomy.