GAZA CITY, Gaza Strip (AP):

Hamas security arrested dozens of supporters of the rival Fatah group, hurled grenades at the home of one Fatah leader, and set up checkpoints across Gaza yesterday, following a mysterious beachside blast that killed five Hamas members and a six-year-old girl.

Hamas leaders blamed Fatah for Friday's explosion, and began the toughest crackdown against the rival group in recent months. A Gaza-based human-rights group reported Hamas security officials arrested at least 160 Fatah loyalists, and some 40 institutions connected to the group were raided.

denial

Fatah leaders denied in-volvement, and an aide to Palestinian President Mahmoud Abbas said the crackdown is reducing prospects for eventual reconciliation.

If Hamas was targeted, it would be the deadliest such attack since the Islamic militants ousted Fatah-allied security forces from Gaza in a violent takeover more than a year ago.

The blast went off underneath a car parked near a crowded Gaza City beach on Friday evening, Hamas officials said. At the time, a group of Hamas activists was picnicking on the beach, Hamas said. The blast shattered the windows of the white sedan and damaged its doors.

Three Hamas members and the girl were killed immediately. Two more Hamas activists died of injuries yesterday and 15 people were wounded, according to a statement by the Palestinian Health Ministry.

Hamas Prime Minister Ismail Haniyeh convened an emergency government meeting yesterday. In a statement released after the meeting, the government said it had instructed authorities "to find the people who were involved in the horrible crime yesterday".

death penalty

The government said those guilty would "be subject to justice in order to be an example for anyone who might think to shed the Palestinian blood". If convicted, the perpetrators could face the death penalty.

Among the dead in the explosion were a senior Hamas field commander and Iyad al-Hayeh, a nephew of Hamas lawmaker Khalil al-Hayeh, health officials said. Osama al-Hayeh, a son of the lawmaker, was wounded.