GAZA CITY, Gaza Strip - Hamas gunmen stormed the home of a local leader from the rival Fatah movement yesterday, witnesses said, sparking a gun battle and capping a day of factional violence across the Gaza Strip that killed at least 13 people, including a 2-year-old boy.

The fighting was among the deadliest in nearly two months and marred the first anniversary of Hamas' upset victory in Palestinian elections. After nightfall, the fighting showed no signs of slowing, as the sound of gunfire echoed throughout Gaza City.

The shooting was concentrated around the home of Mansour Shaleil, a local Fatah leader in the Jebaliya refugee camp just north of Gaza City.

Hamas gunmen surrounded the house early yesterday to detain Shaleil, accusing him of involvement in a shooting that killed two Hamas supporters. After an hours-long standoff, dozens of Hamas gunmen stormed the house and exchanged fire with Shaleil and his supporters, according to witnesses and ambulance drivers.

They withdrew, Palestinian media reported, leaving Shaleil unharmed. Two men identified as Hamas members were killed.

"It looks like they forgot who the enemy is," said Maher Mekdad, a Fatah spokesman. "They forgot the Israeli occupation."

Fatah gunmen, meanwhile, kidnapped 19 Hamas members and threatened to kill them if Shaleil was harmed, officials on both sides said. Their fate was not immediately known after Shaleil's release.

During the day, fighting also spread to the headquarters of the pro-Fatah Preventive Security agency in Gaza City. Four Hamas gunmen were killed in a battle outside a mosque. Hamas accused Fatah gunmen of starting the battle and wounding several worshipers in a drive-by attack. Mortar shells and rocket-propelled grenades were fired in the melee, smashing windows on several homes.

Fighting also erupted outside the homes of Palestinian Authority President Mahmoud Abbas of Fatah and Foreign Minister Mahmoud Zahar of Hamas. Hamas officials said two rocket-propelled grenades damaged Zahar's house.

Hundreds of security forces loyal to Abbas - who was in Europe at the time - were sent into the streets to protect his compound and various security installations.

In all, 13 people were killed throughout Gaza, medical officials said, in addition to two killed just before midnight Thursday. Yesterday's dead included a 2-year-old boy who was shot while traveling in a car in the southern town of Khan Younis. Hamas and Fatah officials accused each other of firing the deadly shot.