JERUSALEM - In the deadliest internecine violence in months, armed Palestinian factions clashed in the streets of the Gaza Strip yesterday, leaving four people dead, more than a dozen wounded, and the future of a unity government in peril.

Running gun battles throughout the day sent residents scurrying for cover and shut down shops as members of Fatah and Hamas attacked each other. There also were reports of kidnappings and counter-kidnappings.

It was the worst outbreak of violence since the rival organizations agreed to a cease-fire at a meeting in Saudi Arabia in February. That truce paved the way for a Palestinian unity government in March, a reconciliation that has proved rocky at best and certainly will come under further strain from yesterday's bloodshed.

The fighting began in the morning when gunmen fatally shot a senior commander of the Al Aqsa Martyrs' Brigade, the armed wing of Fatah. A bystander also was killed.

Fatah blamed the ambush on Hamas, which denied involvement.

The incident triggered a wave of violence throughout the Gaza Strip. Two members of Hamas were killed, Palestinian sources said, including a journalist who the radical group alleged was executed by Fatah gunmen in front of horrified onlookers.

At least 17 people were injured, three critically, hospital officials said. Some of the wounded were hit by gunfire at the funeral for the slain Al-Aqsa commander and at a local mosque. Bullets also flew around the home and office of Palestinian Authority President Mahmoud Abbas, who is a member of Fatah. Abbas was not in Gaza at the time.

Observers urged the warring factions to return to the calm of previous weeks.

"These clashes will only help the enemies of the Palestinian people," said Hamad Bourhan, head of an Egyptian security delegation in Gaza.

But the situation remained tense past nightfall, with some residents too frightened to venture home because of roadblocks where armed men interrogated those going through and searched for members of the opposing group.

Though surprised at the severity of the fighting, many people in Gaza said they had been expecting a violent eruption after a disagreement last week between Hamas and Fatah over a new security plan for the Gaza Strip. Fatah deployed hundreds of its men apparently without consulting Hamas, which sparked some fighting on Friday.

Also yesterday, an expected meeting between Abbas and King Abdullah II of Jordan did not materialize, which the Palestinian leader ascribed to bad weather that prevented the king from traveling to Ramallah. The king had intended to press Abbas on negotiations with Israel and on an Arab peace initiative.