Fatah gunmen on Sunday stormed the offices of the Palestinian Authority Health Ministry in Gaza City and the Nablus Municipality in a sign of growing tensions with Hamas. The latest attacks on the Hamas-controlled offices followed Saturday's clashes between supporters of the two parties at two universities in Gaza City. At least 40 people were wounded. Khaled Madi, a spokesman for the ministry, said several Fatah gunmen stormed the offices of the minister, Bassem Naim, and demanded that he sign a document instructing the Finance Ministry of to cover the medical expenses for some patients abroad. "The gunmen claimed that they were members of Fatah's armed wing, the Aksa Martyrs Brigades," Madi said. "They wanted the minister to give permission to some people to receive medical treatment in Egypt." He said Naim refused to sign the document because a ministry legal committee had determined that it was illegal. "The minister asked the gunmen to return the next day in civilian clothes so he could study their request," he added. "But the gunmen tried to force the minister to sign the document by threatening him with their weapons." According to Madi, while the gunmen were still arguing with Naim, some of their friends who were waiting outside opened fire indiscriminately. Three of the gunmen who were inside the minister's office were wounded. Hamas gunmen who rushed to the ministry managed to apprehend the assailants after a brief exchange of gunfire. Sources in Gaza City said the Hamas gunmen belong to a new force that was established recently by Interior Minister Said Siam. The force consists largely of members of Hamas's armed wing, the Izzaddin al-Kassam Brigades. The sources added that this was the first time that members of the new force had been summoned to protect Hamas leaders in the Gaza Strip. The force was established with the declared goal of assisting the PA security forces in restoring law and order. Earlier, scores of Fatah gunmen occupied the Nablus Municipality building and kicked out all the employees. The gunmen were protesting statements made by Hamas leader Khaled Mashaal over the weekend, in which he accused PA chairman Mahmoud Abbas and Fatah of conspiring with Israel and the US to topple the Hamas cabinet. The gunmen announced that the municipality, which is controlled by Hamas, would remain closed until Mashaal apologized to the Palestinians for insulting Fatah. Nablus Mayor Adli Yaish condemned the attack and called on all the workers to stay in their offices, saying the municipality's job is to provide services to the city's residents and not to serve as a platform for political parties. The gunmen finally agreed to leave the building following the intervention of top Hamas and Fatah leaders in the city. In Jenin, thousands of PA policemen and security officials staged a demonstration against Mashaal and the Hamas cabinet, defying instructions from Abbas banning such protests. Khaled Abu Hilal, spokesman for the PA Interior Ministry, which is responsible for security, condemned the Fatah gunmen who carried out the attacks as "mercenaries" and "immoral." "These gunmen apparently didn't hear about our decision to end all forms of lawlessness and anarchy," he said. "Only criminals are capable of carrying out such imprudent attacks against our people." Israeli defense officials said they were concerned that the internal violence within the Gaza Strip would spill over into Israel in the form of escalated terror activity. "There is certainly a chance the violence there will spill over into Israel," one security official said. "We are watching and are concerned." Fatah's defeat in the recent PA elections and the competition with Hamas have led the long-time dominant political party to increase its involvement in anti-Israel terror activity. "Fatah has stepped up its involvement in terror and is trying to fight with Hamas through Israel," the official said. Yaakov Katz contributed to this report.