Hamas gunmen trying to round up weapons of opponents exchanged fire with members of a powerful clan in the southern Gaza town of Khan Younis on Saturday, a Hamas official and a witness said. The clash erupted between Hamas fighters and the al-Astal clan, the largest in Khan Younis. Since taking control of Gaza earlier this week, Hamas has begun rounding up weapons of rivals, including members of the Fatah-allied security forces. The al-Astals refused to give up their weapons, saying they needed them as defense in clan feuds in the area. A gunfight erupted, and Hamas fighers surrounded four homes of the clan, said Sameh al-Astal, 23, a family member. Islam Shahwan, a spokesman for Hamas, said no exceptions would be made in the weapons roundup. "The point is to collect all illegal weapons from all families." He said Hamas was trying to negotiate an end to the standoff.