ISLAMABAD - A blast on a passenger bus killed at least seven persons in Pakistan's eastern Punjab province Saturday evening, police and local media said.

Around 20 passengers were also injured in the blast near the city of Kharian, some 35 km from Gujrat, a main city in the region. Kharian has the world's second largest army base, built during the British colonial era.

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Express TV reported that three women and a child were among the dead. Police said that around 50 passengers were on board when the blast took place.

Local TV channels reported that it was a suicide blast. But police did not confirm the suicide attack. Eyewitnesses said that the bomb was kept at the back seat of the bus.

Motives behind the blast were unclear as civilians were targeted in the attack. No group has claimed responsibility for the blast.

Residents started rescue operation and shifting the injured people to nearby hospitals. Reports said that the bus caught fire which also spreaded to the nearby wheat crops.

It is the second blast in Pakistan within two days.

Twin suicide attacks killed over 80 security personnel in Pakistan's northwest on Friday. Taliban had claimed responsibility for the bombings which they said that was revenge of the death of al-Qaida chief Osama bin Laden. Over 100 security men and civilians were also injured in the attacks.