"Members of the Ezzedine al-Qassam Brigades were trying to prepare for a Jihad operation," the Islamist movement's armed wing said in a statement.

It said six members of the brigades were killed in the blast in Beit Lahya. A local leader of the Hamas armed wing died of his wounds on Friday, one day after his four-month-old baby died in the explosion, a doctor at Shiffa hospital in Gaza City said.

There have been several cases in the past when militants accidentally set off deadly blasts while assembling makeshift explosive devices.

About 50 people were wounded, among them 15 children, in Thursday's explosion, according to the head of emergency services in Gaza, Muawiya Hassanin.

The blast destroyed a house and damaged about 10 neighbouring homes, witnesses said.

Hamas initially blamed Israeli armed forces, and militants fired dozens of rockets and mortar rounds at Israel in the hours following the explosion.

Israeli forces responded by targeting militants, with medics saying three Hamas fighters were killed in an air raid. Three more militants were killed by Israeli forces earlier Thursday.