A militant commander affiliated with Palestinian Mahmoud Abbas' Fatah movement was shot dead on Sunday, in the most serious attack since Abbas launched a new security plan aimed at calming a wave of violence in the Gaza Strip last week.

Fatah quickly blamed the rival Hamas group, its partner in the Palestinian government, and the dead man's comrades vowed revenge. Hamas denied involvement.

In another sign of the prevailing lawlessness in the coastal strip, three employees of the Gaza electrical company were shot and seriously wounded while driving in a company car in Gaza City, hospital officials and Palestinian security officials said. The employees were out collecting unpaid bills.

The dead militant was identified as 32-year-old Baha Abu Jarad of the pro-Fatah Al Aqsa Martyrs' Brigades. He was shot while driving through the northern Gaza town of Beit Lahiya, and later died of his wounds, hospital officials said. Fatah issued a statement accusing Hamas of the shooting. In a separate message, the Al Aqsa group said it had identified the killers as two local Hamas activists.

"We will go after these killers," the statement said, raising the likelihood of further violence.

Since Israel withdrew from Gaza in 2005, the area has experienced a wave of infighting, armed robberies, deadly family feuds and kidnappings.

Hamas and Fatah formed their unity government in March with the aim of restoring calm. The alliance has brought a lull in factional fighting, but crime and violence remain rampant in Gaza.

However, in recent days, factional tensions have heated up after Abbas ordered 3,000 police to fan out across lawless Gaza City on Thursday without coordinating the deployment with Hamas. The latest round of violence has been the fiercest since Hamas and Fatah teamed up to share power.

Despite the growing tensions, it is unlikely the coalition will break apart soon because neither party can govern alone or is eager to go to elections.