Nine Palestinians were killed and more than 25 were wounded in fierce clashes that erupted between Fatah and Hamas gunmen in the northern Gaza Strip on Monday, Palestinian Authority security sources said. Most of the fighting took place inside a Palestinian hospital in Bet Hanun, the sources added. Fighting between Hamas and Gaza rekindled Monday afternoon- shortly after a truce was declared. The violence began as Hamas gunmen shot and killed Fatah operative Louie el-Massri in a Gaza City skirmish. In response to his slaying, members of Massri's family decided to exact retribution by attacking a Hamas position Beit Hanun, north of Gaza. Two Hamas men were killed in the reprisal. Earlier Monday, gunmen opened fire at the Palestinian Cabinet building while the government was meeting inside, officials said. There were no reports of injuries. An official in Prime Minister Ismail Haniyeh's office said the gunfire didn't disturb the Cabinet meeting, and said officials were trying to pin down the source of fire. The official spoke on condition of anonymity because he was not authorized to speak to the media. Palestinian security and witnesses said rival Hamas and Fatah forces were exchanging fire from neighboring high-rise buildings. Earlier, the office of Palestinian Authority Sports and Culture Minister Bassem Naim was fired upon on Monday afternoon, Israel Radio reported. Naim is a close associate of PA Prime Minister Ismail Haniyeh of Hamas. He was unharmed in the incident. "It was the Fatah gangs. There was no justification. We were at work, and the ministry came under fire," a ministry official, identified only as Ahmed, told the Hamas-affiliated Aqsa Radio. Naim was inside the building at the time, said his sister, Huda. There were no injuries, she said, accusing Fatah of trying to kill her brother. The factions agreed to meet to negotiate a long-term solution after a ceasefire announced Monday morning lasted less than half a day. Overnight Sunday, Gunmen opened fire on the house of Ismail Haniyeh, in the Shati refugee camp next to Gaza City, security officials said. There were no immediate reports of casualties. However, Army Radio reported two Palestinians killed in clashes overnight. The attack on Haniyeh came amid a new wave of violence in Gaza that left four Palestinians dead on Sunday. Shortly after the shooting, Fatah and Hamas leaders called for calm - in large part to allow thousands of high school seniors to take their matriculation exams in peace. "This is shameful for our people," Palestinian President Mahmoud Abbas said during a trip to a school in the West Bank. "I call on everyone to stop this immediately, not only because of the examinations, but also for our people to live a normal life." About 24,000 high-school seniors in Gaza were beginning two weeks of final exams Monday, along with more than 40,000 others in the West Bank. The fighting took a grisly turn on Sunday, when Hamas gunmen kidnapped Muhammad Sawirki, a 24-year-old a member of Abbas's elite presidential guard, took him to the roof of a 15-story apartment building and threw him to his death. That set off skirmishes throughout the city, including gun battles and shelling in which one person was killed and 12 were wounded. The fighting delayed the evacuation of Sawirki's body. Two passersby, an elderly woman and her daughter, managed to drag the body to a secure place before an ambulance took it away. Fatah militants surrounded the house of a Hamas mosque preacher, fired rocket-propelled grenades at the four-story building and then entered, firing at the preacher, and taking him away. Later, his body was brought to a hospital. Hamas pledged revenge. And just before midnight, Hamas activist Husam Abu Kainas, 26, was thrown off the 12th floor of a building and killed, security officials said. Four other Hamas men in the building were shot and wounded, bringing the day's toll to three dead and 36 wounded, medical officials said. A Hamas operative wounded Friday in southern Gaza infighting also died on Sunday. Later, Fatah gunmen shot and killed Muhammad al-Rafati, the imam of the city's Abbas Mosque, who was known for his close links with Hamas. Hamas accused Fatah gunmen of kidnapping one of its members in Deir el-Balah refugee camp in the central Gaza Strip. Fatah accused Hamas of abducting and shooting several Fatah activists in different parts of Gaza. Eyewitnesses said tensions between the two movements escalated over the past few days as each sent gunmen to patrol streets and set up checkpoints.