Khamis Bakr demands revenge. The local Fatah leader's 16-year-old nephew was killed by Hamas gunmen in one of Gaza's recent street battles, and Bakr wants to even the score, despite last week's Saudi-brokered truce between the two rivals. Bakr, 35, said he'll always put the interest of his family before that of his party. Such unfinished business between Gaza's powerful clans is one of the main threats to the power-sharing agreement signed last week in the Muslim holy city of Mecca between the Islamic militant group Hamas and the Fatah movement of the moderate Palestinian president, Mahmoud Abbas. Despite assurances by Hamas and Fatah leaders that they are putting months of deadly factional fighting behind them, resentment and mistrust are still running high and could erupt into violence any time. The nasty graffiti on the smoke-blackened walls of Gaza City's Islamic University, a Hamas stronghold trashed earlier this month by Abbas-allied security forces, reflected the festering anger. "The president's people are destroyers," read one slogan scribbled onto the scorched wall of the computer lab. The attackers, who caused $15 million (â‚¬11.5 million) in damage, according to Hamas, left behind messages of their own, including a spray-painted warning that read: "The Presidential Guard will show no mercy." In Gaza City's beachside neighborhoods, hardest hit by the battles, life has largely returned to normal since Thursday's agreement in Mecca. On a recent day, streets were congested, shops opened, and members of the security forces lounged in plastic garden chairs on sidewalks, rather than standing nervous watch behind sandbags. One motorist washed his car on the street in a show of optimism and some residents ordered glass to replace broken windows. But no one was relaxing too much yet. Huge metal tripods retrieved from the Gaza City marina blocked roads near Abbas' compound to keep away cars. In the ocean-view Rimal neighborhood, the owners of a 14-story apartment high-rise added three more rows of cement blocks to their garden wall and installed a large metal gate to keep out gunmen. During the last round of fighting, Hamas militiamen took over the rooftop of the high-rise as part of a race between rival groups for control of strategic positions. Iman Husseini, one of the residents of the building, said she had pleaded with the gunmen to leave, to no avail. At one point, the Hamas fighters opened fire on Abbas-allied Force 17 officers at a gas station across the street, killing a 16-year-old bystander, Mohammed Bakr, according to the victim's relatives. The shooting triggered three days of clashes between the Hamas men on the roof and members of the Bakr clan, most allied with Fatah. The 3,500-strong Bakr clan lives in several blocks near the high-rise, and during the fighting set up makeshift roadblocks at the entrances to neighborhood alleys to control traffic. Khamis Bakr, the local Fatah leader, said Saturday that despite the Mecca truce, the clan will not rest until justice is done. "We are happy with the agreement," Bakr said. "We hope that our son will be the last victim. But the family still wants the blood of Mohammed to be avenged. Hamas has to hand over the killers, either to the family or to a court." With Gaza's judiciary barely functioning, it is unlikely any of those involved in killings would be brought before a court. Factions would also balk at handing over their fighters, particularly since it would be almost impossible to determine who did what in the chaotic battles. Another option is to pay compensation to the bereaved families, in line with Islamic law. In Gaza, the going rate per victim is 33,000 Jordanian dinars ($47,000, â‚¬36,000), based on local Islamic customs. Prime Minister Ismail Haniyeh of Hamas said in a speech last month that the families of victims could be compensated. Bakr declined to say what steps he might take to avenge the death of his nephew. Leaders from Hamas, Fatah and smaller factions acknowledged Saturday that clan revenge for dozens of victims could easily bring down the Mecca agreement. "Hamas and Fatah have agreed to halt their fire, and that's a beginning, but now they must hurry" to quell possible revenge acts, said Khaled Batch, a leader of the small Islamic Jihad group not involved in the fighting. Islamic Jihad said it has already settled eight family claims involving killings. Abbas on Friday announced the formation of a reconciliation committee to address unsettled scores. "It is important to deal with the families," said Tawfiq Abu Khoussa, a Fatah spokesman. Both Abu Khoussa and Hamas spokesman Ismail Radwan said they were confident the two factions can keep their supporters in line. In coming days, Abbas and Haniyeh are to move quickly to form a coalition government. Under the deal signed in Mecca, Hamas gets nine Cabinet seats, Fatah gets six, independents are given five portfolios and small factions get four. Haniyeh remains prime minister. Once a government is in place, possibly before the end of the month, the volatile situation could begin to stabilize. Palestinian analyst Nasser Allaham said Hamas and Fatah have strong incentives to keep the peace because voters fed up with the fighting would punish anyone believed to be sabotaging the power-sharing deal. However, the deal could unravel if Israel and the international community refuse to lift a crippling aid boycott, citing the power sharing agreement's failure to meet international demands for Hamas to recognize Israel. And after countless broken cease-fires, skepticism in the Palestinians territories remains strong. "There is a lot of mistrust," said Bakr, the local Fatah chief. "If it (the Mecca deal) lasts for six months, it is a good agreement."