Multiple casualties reported after explosion on a bus in Jerusalem

An explosion aboard a bus in Jerusalem caused around 20 casualties on Monday, Israeli media said.

Police are investigating whether the explosion came from a bomb or was simply the result of a technical malfunction.

"Initial assessments say this is likely not a terror attack," Israeli news outlet Ynet reported. The bus was reportedly empty when it exploded, but many people on an adjacent bus apparently suffered burns in the explosion.

Television images showed smoke billowing from a burned-out bus on Derech Hebron, in southwest Jerusalem. It was not immediately clear if the casualties were dead or wounded. 

This story is developing.