Dahlan's relative, an officer in the Preventive Security Service, was married in the presence of many of his family members and friends. The explosion took place as he was getting on the stage.
The injured are all family members and Fatah activists who attended the wedding. According to estimates, the blast was caused by a grenade. Eyewitnesses reported seeing veiled people hurling a grenade at the crowd.
A Gaza source told Ynet that the explosion was not caused by a grenade, but by an explosive charge placed under the stage on which the bridegroom was sitting and the guests were dancing.
"There was another device which did not explode. Had it been detonated, no one would have escaped alive," the source said.
The Palestinian police in the Strip, which belongs to Hamas, launched an investigation into the incident. Fatah officials accused Hamas members of hurling the grenade. They added that the real number of injured was almost 60.
A Hamas security source told Ynet, however, that "Hamas has nothing to do with this" and that one of the leads being looked into was an internal dispute which led to the incident.
Officially, the Hamas interior ministry said the explosion was the result of a shock grenade which led to shrapnel flying all over the stage. The ministry stressed that using fireworks and torches was in violation of the law.
Dahlan's people have been the target of Hamas threats in the past few years, following the tension between the rival factions. In January 2007, Hamas gunmen tried to kill Dahlan's bodyguard. About two years ago, Hamas accused Dahlan of being responsible for an attempt to assassinate the organization's prime minister in Gaza, Ismail Haniyeh, whose son was injured in the incident.
Hamas has also accused Dahlan of arresting group members and torturing them during his tenure as head of the Preventive Security Service in the 1990s. Dahlan had launched a battle against Hamas gunmen following a series of suicide bombings in Israel in 1996.