A massive explosion Friday ripped through the crowd at a rally staged by the Palestinian militant group Hamas in the Gaza Strip, killing at least 15 Palestinians and wounding scores of others, medical officials said.
Hamas blamed Israel, which denied any involvement in the blast.
Witness accounts and some Palestinian Authority officials suggested that ordnance and weaponry being paraded by the group had accidentally gone off.
But the incident set off a series of attacks and reprisals.
Palestinian militants fired 21 crude rockets overnight at the Israeli town of Sderot just outside Gaza, causing five injuries, most of them minor.
Before dawn today, Israeli aircraft attacked three buildings in and near Gaza City that the military described as Hamas weapons manufacturing or storage sites.
Palestinian officials reported several minor injuries in the explosions.
Palestinian Authority President Mahmoud Abbas has been struggling to keep order in Gaza since Israel’s military withdrawal from the territory early this month. But factional fighting and general lawlessness have persisted.
The deadly explosion at the rally took place at nightfall during a procession through the densely populated Jabaliya refugee camp on the edge of Gaza City.
Masked fighters marched or rode in a convoy of vehicles that wound through the camp’s narrow streets.
At least two children were believed to be among the dead. It is not unusual for Palestinian parents to take small children to Hamas rallies, sometimes holding them aloft for a better view of the spectacle.
Witnesses said the blast originated in a truck that appeared to have been carrying homemade Kassam rockets. The vehicle was left a twisted, charred mass of metal.
Ahmed Rajab, a 35-year-old from Jabaliya, said he was watching the procession from 15 to 20 yards away.
Those standing close to the truck were maimed by flying metal and the force of the explosion, he said.
“The sound of it was huge,” he said. “First I ran to get away, then I ran back and helped carry people who were hurt to ambulances.”
Hamas spokesmen accused Israel of having staged an airstrike on the rally.
However, a spokesman for the Israel Defense Forces, speaking on condition of anonymity, said flatly, “The IDF had no connection of any kind to this incident.”
Israel, which has used pinpoint missile strikes to kill most of Hamas’ top leaders in Gaza over the last two years, declared more than six months ago that it would target only “ticking bombs,” a reference to those planning imminent attacks.
The explosion came hours after Islamic Jihad militants fired rockets that fell harmlessly into Israel. The group said the strikes were in retaliation for the killing of three of its members in a predawn raid in the West Bank town of Tulkarm.
Islamic Jihad has abandoned an informal truce declared in February by the main Palestinian militant factions, but Hamas has largely adhered to it.
The Hamas rally was timed to take place before a ban beginning this evening on the parading of weapons in public. All the militant factions have agreed to abide by the rule.
Hamas said that at least three members of its military wing were among the dead and that the fatalities would be avenged.
“We know very well that our enemy [Israel] is responsible for killing our sons and brothers today,” Hamas official Nizar Rayam told reporters in Gaza City. “There will be a response, in the time and place of our choosing.”
Accidents involving the mishandling of explosives are not uncommon among Palestinian militant factions. This month, five people were killed in a blast in what was apparently a weapons lab in a Hamas-dominated neighborhood of Gaza City.
Times special correspondent Fayed abu Shammalah in Gaza City contributed to this report.