JERUSALEM — At least 21 people are reported injured in an explosion Monday afternoon on a public bus in Jerusalem that police have now confirmed was a terror attack.

Two of the injured in the explosion on Derech Hebron Road, in the Talpiot neighbourhood southern Jerusalem, are in serious condition.

Police say that a bomb was placed in the engine of the bus, which is considered a more sophisticated way to attack, Israel’s Channel 1 reported.

A second bus and a private vehicle reportedly caught fire in the explosion.

The bus reportedly was empty at the time of the explosion. The injured were on the second bus that caught fire.

The injured were taken to three Jerusalem-area hospitals.

Jerusalem mayor Nir Barkat told Channel 1 that the blast came from a small explosive that was on the back of the bus, which was later confirmed by Jerusalem police chief Yarom Halevy. “When a bomb explodes on a bus it is a terror attack,” he said.

A spokesperson for Israel’s fire service reiterated that the blast came from inside one of the vehicles. “This is definitely an irregular incident,” the spokesperson said.

“All avenues of investigation are being followed,” a police spokesperson added.

Speaking Monday night, Israeli Prime Minister Benjamin Netanyahu said Israel would “settle the score” with whoever’s responsible for the attack, though terror groups have yet to claim responsibility.

Hamas lauded the perpetrators behind the attack, but did not take credit. “Hamas blesses the Jerusalem operation, and considers it a natural reaction to Israeli crimes, especially field executions and the desecration of Al-Aqsa Mosque,” the terror group said.