At least 20 killed in a suicide terrorist attack on a civilian bus in Jerusalem, Israel

A bus exploded in Jerusalem on Monday, wounding at least 21 people in what police said was a "terror attack," raising fears of a return to the Palestinian suicide bombings that ravaged Israeli cities a decade ago.

"There is no doubt that this was a terror attack," Jerusalem police commissioner Yoram Halevy said. He said it was too early to know the identity of the attacker or if it was a suicide bombing.

"We are investigating where the explosive device came from, who planted it, how it got on the bus. All this is in the initial stages of investigation," he said.

Police spokesman Micky Rosenfeld said 21 people were wounded in the attack, two seriously, seven moderately and the rest lightly. Another bus and a car nearby were also damaged by the explosion.