A senior Hamas commander and his assistant have been killed in an apparent Israeli air strike in Gaza City that ripped apart their motorcycle.
A bystander also died and seven others were wounded, including a woman and three children, hospital officials said.
Wael Nassar a top Hamas commander, and his assistant, Mohammed Sarsour, were on the motorcycle when it exploded, witnesses said.
Hamas accused Israel of a "cowardly assassination crime".
It was not immediately clear what caused the explosion. Witnesses said they saw a flash in the sky and then the motorcycle exploded, indicating an Israeli missile strike. The residents said they did not see any Israeli helicopters in the sky, though they heard an unmanned Israeli plane.
The Israeli military refused to comment.
The explosion was in the Zeitoun neighbourhood, scene of heavy fighting between Israeli forces and Palestinians earlier this month, after Palestinians blew up an Israeli armoured personnel carrier, killing six soldiers.
Hamas spokesman Sami Abu Zohri accused Israel of a "cowardly assassination crime", part of Israel's "bloody escalation" against the Palestinians.
One of Nassar's brothers was killed when Israeli forces assassinated Hamas leader Abdel Aziz Rantisi on April 17, and seven other relatives were killed in earlier clashes with Israeli forces, Palestinians said.