The first bombing on an Israeli bus in years appears to be an act of terrorism, police said.
The explosion, which injured 21 people late Monday afternoon in Jerusalem, took place days before the Jewish Passover holiday.
‘‘Police are working carefully to rule out that it wasn’t a criminal incident,’’ police spokesman Micky Rosenfeld said, ‘‘but the main direction is that it was a terrorist attack.’’
The device went off at the back of a city bus near the engine, blowing up the gas tank and engulfing the vehicle in flames, Rosenfeld said. Israel Radio said the cause appeared to be an improvised bomb.
One reason police were unable to conclusively determine if the bombing was politically motivated is that the identity of the bomber wasn’t known, Rosenfeld said. Media speculated it might be an unidentified man hospitalized in a Jerusalem medical center with severe wounds.
The blast occurred a week after Prime Minister Benjamin Netanyahu reported a sharp decline in the wave of stabbings, shootings, and hit-and-runs that have swept Israel since October. It brought back memories of the wave of bus bombings that killed hundreds of Israelis in the second Palestinian uprising against Israel.
While police were still pursuing their investigation, Netanyahu pronounced the explosion a terrorist attack.
‘‘We will settle accounts with these terrorists,’’ Netanyahu said late Monday in remarks sent from his office by text message. ‘‘We will locate whoever assembled this bomb, we will reach the dispatchers, and we will get to whoever stands behind them.’’