Attacks on children are unusual in Pakistan, but the blast comes during an upsurge of sectarian violence [AFP]

A bomb has hit a school bus in the Pakistani city of Peshawar, killing a passer-by and wounding four people, including two pupils who were travelling on board.

City officials said the bomb had been hidden in a dust-bin on the roadside, and exploded when the bus stopped.

"When I saw the smoke, I ran towards my teachers at the back [of the bus]," one of the wounded children told Reuters news agency following Monday's attack.

"The teachers said 'come, come'. So we got off the bus," said six-year-old Eman, speaking from a hospital where she was lying on a bed with her head bandaged.

The driver of the bus was also wounded in the attack. He described a "sudden explosion" shortly after some of the teachers had stepped off the bus. "After that I did not have my senses. I fell," he said.  

'Increased violence'

Al Jazeera's Zeina Khodr, reporting from Pakistan, said that there had been increased violence in the area in recent days.

"A senior minister said this was aimed at diverting the attention of security forces, because it is a sensitive time," she said. 

"It is the month of Moharram when traditionally sectarian violence surges. In the past days there has been a upsurge in violence."

Moharram is the holiest month for Shia Muslims.

Iftikhar Firdous, a Pakistani journalist based in Peshawar, said that the incident did not fit the pattern of previous attacks on schools. "This is one of the first incidents where a school bus has been attacked.

Usually the schools have been blown up at night," he said, referring to previous attack on educational establishments that educate girls.

Two suspects were detained at the scene. A police official said the bomb may have been intended for one of the police patrols that frequently pass by the area.

Pakistan has been hit by an increasing number of sectarian attacks in recent years, with government  security forces also being targeted by armed fighters opposed to co-operation with US forces in the region.

Source: Al Jazeera and agencies.