Four Palestinian activists and a five-year-old girl were killed overnight in an explosion near a beach outside Gaza City, officials at the Shifa hospital said.

The activists killed in the blast were members of the Islamist Hamas's armed wing, the Ezzedine al-Qassam Brigades, they said.

The blast apparently occurred near a car in which they were riding but the cause of the explosion was not immediately known.

Hospital officials said 15 Palestinians were wounded.

The activists were identified as Iyad al-Aya, Amir Al-Sabeh, Nidal Moubeihed and Oussama Alhelo.

A Hamas leader, Hallil al-Aya, and the Ezzedine al-Qassam Brigades accused Palestinian "groups who cooperate with the (Israeli) enemy" of being responsible for the explosion.

"These groups are trying to undermine the security of the Palestinian people and are thereby helping the enemy," Aya told AFP, calling on Hamas officials and fighters to be careful.

Aya and the Ezzedine al-Qassam Brigades did not directly accuse Palestinian president Mahmud Abbas' Fatah movement of having been involved in the attack.

Hamas seized power in the impoverished coastal strip a year ago after routing Fatah-led security forces in a week of bloody street battles.

AFP