Gunmen loyal to Palestinian President Mahmoud Abbas of Fatah opened fire on Hamas members in the occupied West Bank on Friday (December 22), shortly after Palestinian Prime Minister Ismail Haniyeh called on militants to maintain calm in Gaza. The fire exchange in the West Bank city of Nablus wounded at least nine civilians, hospital officials and witnesses said. Gunmen of the Al-Aqsa Martyrs Brigades, one of Fatah's armed groups, took to the streets as thousands of Hamas activists and militants attended a rally in the city of Nablus. Armed and masked militants stopped a bus in the middle of the road, aiming rifles at the driver, and fired towards Hamas protesters who spread in the streets after the rally was over. Later, a group of masked gunmen who identified themselves as part of the Al-Aqsa Martyrs Brigades, abducted three Hamas members but released them shortly after. It was the worst violence in the West Bank since Abbas last week threw down the gauntlet to the Hamas government by calling for fresh parliamentary and presidential elections. Days of violence earlier this week in the Gaza Strip killed 10 people. A Fatah official told Reuters that the Hamas Islamist chose to hold the rally despite what he said was an earlier agreement to delay it. Haniyeh, a senior Hamas leader, called for an end to the violence while speaking after Friday prayers in Gaza City. "We continue to stress that all parties must abide by the reconciliation ... agreement. We should continue to restrain ourselves in order to preserve Palestinian blood and reinforce national unity," Haniyeh said. The two sides agreed on a truce in Gaza earlier this week that has largely held. Hamas, which is sworn to Israel's destruction, defeated Abbas's long-dominant Fatah party in elections in January. Hamas has rejected Abbas's call for fresh elections and said such a move amounted to a "coup". Abbas made his election call after talks on forming a unity between Fatah and Hamas collapsed. The aim had been to establish a cabinet that could end Western isolation of the government.