A low-intensity bomb attack in Pakistan's biggest city of Karachi on Saturday wounded two people and caused panic, police said.

The remote-controlled roadside bomb exploded close to the site where a Friday bomb attack killed three soldiers from the Pakistan Rangers paramilitary force.

Police said the target of the attack was not immediately clear, but the bomb exploded when a vehicle of Pakistan Rangers was passing near Karachi University.

"It was a planted bomb. Two passers-by were injured," Salam Sheikh, a senior police officer, told AFP.

A spokesman for the Pakistan Rangers said that troops remained unhurt in the incident.

No one has so far claimed responsibility for the attack, but nearly 4,700 people have been killed across Pakistan in attacks blamed on Taliban and other Al-Qaeda-linked networks since government troops stormed a radical mosque in Islamabad in 2007.

Pakistan's economic hub, Karachi has also recently faced its worst ethnic- and politically-linked unrest in 16 years, with more than 100 people killed in one week alone in October.

The Pakistan Rangers are helping police try to maintain peace in the city.