Gaza City, Gaza Strip ? Fatah and Hamas gunmen attacked two universities and a radio station Friday in the deadliest single day of their violent power struggle. With the death toll climbing to 17 – including four children – the two sides declared another truce.

But they said they needed time to pull their volatile forces off the streets, and fierce gunbattles raged across Gaza in the hours after the announcement.

A cease-fire declared earlier in the week collapsed Thursday, and gunmen armed with mortar shells, rockets and heavy guns traded fire across the Gaza Strip. In all, two dozen Palestinians were killed and some 250 were wounded in the fighting.

In Washington, the so-called Quartet of Mideast negotiators met Friday to explore ways to jump-start peacemaking despite the violence among Palestinian factions.

“There’s simply no reason to avoid the subject of how we get to a Palestinian state,” Secretary of State Condoleezza Rice said after meeting with foreign ministers from the European Union, United Nations and Russia.

Frightened Gazans huddled in their homes Friday as gunmen battled in the streets. Civilians who did venture outside took cover from the crossfire at the entrances to shuttered stores, or cowered behind walls.

Casualties were so high that hospitals ran out of ambulances and people were forced to evacuate the wounded in private cars, carrying bloodied victims in their arms to the emergency room. One man carried in a boy who was shot in the head and later died of his wounds.

Health officials appealed for blood donors, saying they were running out of supplies.

More than 100 Palestinians have been killed in internal violence since the Islamic militant Hamas, which rejects Israel’s right to exist, won parliamentary elections last year and ousted Palestinian President Mahmoud Abbas’ more moderate Fatah movement from power.