Gaza Strip ? Hamas gunmen stormed the home of a militant from the rival Fatah movement Friday, witnesses said, sparking a deadly gunbattle 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 heaviest 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 home early Friday to detain Shaleil, accusing him of involvement in a shooting that killed two Hamas supporters. After an hourslong standoff, dozens of Hamas gunmen stormed the house and exchanged fire with Shaleil and his supporter, according to witnesses and ambulance drivers.

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