Palestinian security demanding overdue salaries from the Hamas government blocked main Gaza Strip intersections on Sunday and forced shopkeepers to shutter their stores, in the widening faceoff between the ruling party and forces loyal to Palestinian President Mahmoud Abbas.

Security officers affiliated with Abbas' Fatah party set tires ablaze on main highways, snarling traffic and sending black smoke billowing over Gaza. Fatah security forces, some dressed in camouflage, forcibly shut down Gaza shops, shooting up lighting, facades and displays of shops that refused to abide by the strike.

The unrest came just hours after a senior Fatah activist was killed early Sunday in a gunbattle with Hamas militia. Fighting near the Bureij and Nusseirat refugee camps in central Gaza began over the weekend after Fatah police demonstrated to demand salaries on the eve of a major Muslim holiday.

Fatah vowed to further escalate the unrest before and after the three-day Eid el-Fitr festivities, which begin Monday.

Tensions between the two factions have been rising since the Islamic Hamas, which is committed to Israel's destruction, unseated the long-ruling Fatah in January parliamentary elections.

The Hamas government, choked by international sanctions meant to force it to moderate, has been largely unable to pay 165,000 state workers — half of them security forces — since taking office in March. Nevertheless, it has refused to ease its hardline stand against Israel and join with the more moderate Fatah in a coalition government that would recognize the Jewish state.

Fatah and Hamas are also at loggerheads over control of the security forces, which are for the most part under Fatah's control. Hamas formed its own 6,000-member militia several months ago, raising the stakes in the often-violent battle between the two.

On Saturday, Abbas brought a security commander out of retirement to block Hamas from building up its forces in the West Bank — another sign that the standoff between the Islamic militants and Fatah could erupt into widespread violence.

The commander, Ismail Jaber, is tainted by corruption but holds sway over key West Bank commanders. He is seen as one of the few people who can unify pro-Fatah forces in the West Bank, which have been riven by infighting and rivalries.

Jaber was appointed a day after Palestinian Foreign Minister Mahmoud Zahar said the Hamas militia would be reinforced in the West Bank, Fatah's stronghold. A Hamas official said they planned to recruit about 1,500 members there.

Adding to Fatah's concerns, Hamas officials said Iran has promised to help train their security forces.