At least 15 Palestinians have been killed and scores injured in a blast during a parade by the militant Hamas group in the Gaza Strip.
The truck was surrounded by people when the blast happened
A truck carrying gunmen and home-made weapons blew up during the rally in the Jabaliya refugee camp in northern Gaza.
Israel has denied involvement, while the ruling Palestinian Fatah faction said it held Hamas responsible.
It is the deadliest incident in Gaza since Israel pulled its troops and settlers out earlier this month.
Hours earlier, Palestinians fired rockets into Israel from Gaza after Israel killed three militants in a raid in the West Bank town of Tulkarm.
The rockets did not cause any casualties.
People in pieces
Palestinian witnesses said a crowd, including many children, swarmed round the truck moments before the explosion.
Video filmed during the rally showed a large cloud of white smoke rising into the sky, as hundreds of people ran from the scene of the blast.
The pictures also showed several badly injured bodies on the ground.
An unnamed witness was quoted by Reuters news agency as saying "I was thrown several metres, then I looked behind and I saw people dismembered and lying on the ground dead."
The Associated Press news agency quoted another man, who gave his name as Hussam, as saying he helped pull three men out of the truck, two dead and one alive but with a severed leg.
Hamas accused Israel of causing the blast and vowed revenge.
However Palestinian leader Mahmoud Abbas' Fatah faction said it held Hamas "fully responsible for the victims of the military parade [that was held] among civilians".
Israel has denied any involvement in the blast.
Earlier, Islamic jihad militants fired a volley of rockets into Israel in what they said was retaliation after Israel killed three militants in Tulkarm.
Israel said the militants were killed after opening fire on troops who were trying to arrest them.
The BBC's James Reynolds in Jerusalem says the latest incidents are a sign of high tension in the Gaza Strip even after the Israeli withdrawal.