Israeli Prime Minister Benjamin Netanyahu pledged to find and punish the 'terrorists' behind an explosion in a bus in Jerusalem.

The prime minister called the attack an act of terrorism though the police did not term the incident a terror attack.

"We will find whoever prepared and dispatched the explosives, as well as those who helped them. We will settle accounts with those terrorists," Netanyahu said, according to the Jerusalem Post.

As many as 21 people were injured as a bomb ripped through a bus in Jerusalem on Monday. At least one person was in critical condition after the bomb exploded in the bus plying in an industrial area in Talpiot neighborhood.

Police confirmed the blast was ignited by an explosive device. "What we confirmed is that the remains of an explosive device were found on one of the buses," police spokesman Micky Rosenfeld said.

"We are still questioning people who are in the hospital to determine what happened moments before the explosion... We're working carefully and cautiously to confirm whether it was a terrorist attack," he said, according to JPost.

The blast caused a huge blaze, with another bus behind also catching fire. Emergency teams took half an hour to put out the blaze.