Security personnel found the body of a pro-Palestinian activist from Italy who was killed and left in an abandoned house in the Gaza Strip following his abduction by militants, Hamas said on Friday.
Two men were arrested and others were being sought in the killing of Vittorio Arrigoni, officials added, insisting that Hamas's grip on the beleaguered coastal enclave remained intact. One official said he had been strangled.
"The goal of this depraved band of outlaws was to spread chaos and anarchy in the Gaza Strip, a desperate attempt to strike at the stable security situation," Hamas spokesman Fawzi Barhoum said.
A Jihadist Salafi group in Gaza aligned with Al Qaeda had threatened on Thursday to execute Arrigoni by 5 pm (1400 GMT) unless their leader, arrested by Hamas last month, was freed.
"A security force entered a house and they found the Italian man's body, he is dead," a Hamas security official told Reuters.
In Rome, the Italian Foreign Ministry said consular officials had confirmed the body was that of Arrigoni.
Saeb Erekat, an aide to US-backed Palestinian President Mahmoud Abbas, whose Fatah faction was driven out of Gaza by Islamist Hamas in 2007, called the killing "a dark page in Palestinian history" and appealed for national reconciliation.
Arrigoni, 36, was a blogger who had lived in Gaza since arriving in August 2008 aboard a humanitarian aid boat that Israel admitted despite imposing a blockade on the territory.
Hamas vehemently opposes Salafists who espouse a more extreme form of Islam and appear to be attracting recruits -- including from Hamas.
Although it shares Al Qaeda's enmity toward the Israeli state, Hamas has aroused Salafist anger by broaching truces with the militarily superior Israelis and exploring political accommodation with secular Palestinian rivals like Abbas.
The Salafists see Hamas as insufficiently zealous in enforcing Islamic law, have attacked Internet cafes and want Christians expelled. Palestinian and Israeli analysts believe some are foreigners who slipped in through neighbouring Egypt.
Ehab Al-Ghssain, spokesman for the Hamas Interior Ministry, told a news conference the arrest and questioning of one of the group had led to the discovery of where Arrigoni was being held.
"The forces moved quickly and wisely to the place but found that the abducted man was killed hours earlier in an ugly manner, according to the pathologist," Ghssain said.
Arrigoni had been strangled, the security official said.
Ghssain said the abductors had rented the house where the body was found and had used someone else's car to try to conceal their identities.
"Their intention from the very beginning was to kill their victim, because the crime took place after a short period of his abduction," he said.
In a YouTube clip posted earlier by his abductors, Arrigoni was shown blindfolded with blood around his right eye. A hand was seen pulling his head up by his hair to face the camera.
The accompanying Arabic text said: "The Italian hostage entered our land only to spread corruption." It described Italy as "the infidel state".
Arrigoni was the first foreign national to be abducted in Gaza since BBC journalist Alan Johnston, who was held for 114 days by an Al Qaeda-inspired group called the Army of Islam. He was released in 2007.
Barhoum said the killing could dovetail with Israel's bids to isolate Gaza. International activists plan to sail as many as 15 ships there next month, defying the Israeli navy's closure.