A motorcycle bomb has ripped through a university bus in south western Pakistan, killing four students and injuring 50 people, a police spokesman said.
Qazi Abdul Wahid said today's bombing targeted a bus belonging to the Baluchistan IT university.
The attack took place in a neighbourhood of the provincial capital, Quetta.
Mr Wahid would not say who was suspected in the attack but security agencies hold Baloch nationalists responsible for such bombings.
Baluchistan has witnessed a decades-long insurgency by renegade tribal elders and Baloch nationalists who demand greater autonomy and a larger share of the province's resources such as natural gas and minerals.
The province borders Afghanistan and Iran and is also believed to be a refuge for Taliban and Pakistani militants.