A blast went off in the house of a senior Islamic Jihad activist Friday, killing him and at least five people and wounding 40, medics and Hamas police said.
At least 40 people were hurt, including nine who were in critical condition, Health Ministry official Moawiya Hassanain said.
Witnesses said the three-story home of Ayman Atallah Fayed was flattened by the blast, and that six nearby homes were badly damaged.
Islamic Jihad claimed Israeli warplanes hit the house in an airstrike, but Hamas police said the cause of the blast was not clear.
Islamic Jihad said Fayed was among the dead, and that the group would carry out reprisal attacks against Israel.
Fayed was a senior member of the Islamic Jihad military wing. Israel routinely targets top militants in airstrikes, but the Israeli military said it had no knowledge of any strike in Bureij.