Tel Aviv bus explosion! Casualties reported.

At least fifteen casualties have been reported as a bus exploded in Tel Aviv.

Ambulances have been on the scene, according to police in Israel, who are calling the explosion a "terrorist attack".

Television showed pictures of a smoke-filled bus, with its windows broken.

Israeli Police spokesperson, Mickey Rosenfeld told Al Jazeera: "There are at least 15 people who are injured, we know of three people who are moderately injured."

"We do believe it was a terrorist attack," said Rosenfeld.

There was an apparent explosion on a bus in Shaul HaMelech Street in Tel Aviv, "

Most of the injured suffered only mild injuries," said Ofir Gendelman, a spokesman for Prime Minister Benjamin Netanyahu.

"The background and circumstances are not clear yet," police spokeswoman Luba Samri told the AFP news agency.

Al Jazeera's Tom Ackerman, reporting from Jerusalem, says: "The location of the explosion was a block away from the Israel defence building".

The attack happened on the eighth day of an Israeli offensive against the Gaza Strip which Israel say they have launched with the stated aim of preventing rocket strikes from the strip.

Celebratory gunfire rang out in Gaza City when local radio stations reported news of the Tel Aviv explosion.