The Gaza Strip's Hamas rulers on Saturday declared a ban on public rallies by the rival Fatah movement in a fresh move to tighten their hold on power, but Fatah officials vowed to defy the order and go ahead with planned marches to celebrate the movement's 43rd anniversary next week. Hamas, which violently seized control of Gaza in June from Fatah-affiliated security forces loyal to Palestinian Authority President Mahmoud Abbas, has been stepping up pressure on Fatah members ahead of the anniversary celebrations, planned to begin on Dec.31 and to last until Jan. 3. Scores of Fatah student activists were rounded up late Friday inside Gaza City's Al-Azhar university, accused by Hamas of plotting to foment public disorder from inside the Fatah-affiliated institution. Salem al-Rifi, 21, who was held for nine hours, said some 25 other students were detained with him. They were told to sign a pledge not to participate in any Fatah rallies or face jail and a fine. Most of them were released before morning after interrogation and warnings. Rifi said posters, paints, balloons and flags intended for use in Fatah anniversary events were confiscated from the students, along with their mobile phones. "When they arrest us, we become more determined," he said. "It means we are doing something right." When Fatah last staged a mass show of opposition in Gaza, with a rally of 250,000 supporters on Nov.12, Hamas security men cracked down hard, killing eight marchers and injuring 85. Hamas blamed Fatah for instigating the violence. However, human rights groups and participants in that rally said Hamas used excessive force against the protesters. There were no recorded injuries to Hamas personnel. Fahmi Zaarir, a Fatah spokesman in the Abbas-controlled West Bank said the movement would hold rallies in Gaza next week, regardless of the latest order. "We will defy Hamas decisions by planning popular activities in all of Gaza," he said. Jamal al-Jarrah, a senior Hamas security official, said the restrictions had been ordered in the interests of public safety. "The ban is to protect civilian lives," Jarrah told a Hamas-backed Gaza newspaper. "They (Fatah members) want to kill and terrorize citizens in such rallies." Hamas has been struggling to keep Gaza from sinking deeper into poverty and to calm dissent. Since its takeover, the coastal strip has been virtually cut off from the world, with neighboring Israel and Egypt keeping a tight squeeze on borders, restricting passage of people and goods. At the same time Abbas's western-leaning government has won international support, further marginalizing Hamas rule in Gaza. In his West Bank power-base, Abbas banned a Hamas 20th anniversary rally earlier this month and Hamas at the time said it would do likewise and prevent Fatah rallies in Gaza. The Abbas government has relaunched peace talks with Israel after a seven-year hiatus, but despite international support, Abbas faces many domestic challenges, including seeking to rein in militants, both in the West Bank and also in Gaza, over which he has no control.