The number of injured in a bomb blast at a shopping mall in Turkey's capital Ankara on Tuesday has risen to 100, authorities said on Wednesday, while police searched for clues as to who was behind the attack.

"We have seen a vicious, ruthless terror attack at Ankara's busiest time," said Prime Minister Recep Tayyip Erdogan, who was visiting the scene.

The blast occurred during evening rush hour at the entrance to a shopping center in the district of Ulus. A Pakistan national was among the dead. The area has been cordoned off and an investigation has begun. Unconfirmed reports suggest an explosive device may have been left at a nearby bus stop.

Much of the front of one building was ripped off by the blast at the Anafartalar shopping center. TV footage showed several people lying seriously injured on the pavement surrounded by piles of concrete and glass. Other people, possibly passers-by, were hurt by flying glass.

Turkey has been hit by bombings in recent years. Some have been blamed on Kurds and others on Islamic militants.

In November 2003, more than 60 people were killed by a series of suicide bombings in Istanbul which the authorities linked to al-Qaeda.

Kurdish rebels carried out a spate of attacks on tourist sites in Turkey last year, killing more than a dozen people, BBC reports.