Hamas forces killed two of the alleged murderers of Italian International Solidarity Movement (ISM) activist Vittorio Arrigoni in a shoot-out in Gaza last week.
Arrigoni, who spent nearly three years in Gaza, was kidnapped and murdered by a Salafist group, opposed to Hamas, in retaliation for the imprisonment of the movement's leader.
Arrigoni was a leading member of ISM, a radical pro-Palestinian organisation whose members live in Palestinian towns and villages in the West Bank and the Gaza Strip.
He was kidnapped in Gaza on April 15. A YouTube video, released by the Tawhid and Jihad group, showed him tied up and blindfolded having been beaten up.
The organisation demanded Hamas release its leader within 30 hours, or Arrigoni, who was accused of "spreading corruption" in Gaza, would be executed. Hamas members stormed the house where he was being held a few hours later but he had already been hanged.
Tawhid and Jihad, a Salafist group with ties to Al-Qaida, has been waging a campaign of terror attacks in Sinai since 2006 and, in the past two years, has been challenging Hamas's rule in Gaza. The group also launched rocket attacks against Israel in recent months, despite Hamas's intermittent attempts to hold a ceasefire with Israel.
While the street battles between Tawhid and Jihad and Hamas were relatively low-profile until the past few weeks, the organisation decided to retaliate by killing a foreigner after Hamas arrested its leader, Hesham
al-Saidni, last month.
Following Arrigoni's murder, Hamas published the photographs of his three alleged killers and, last Tuesday, attacked a house where they were hiding, killing two of them and wounding and arresting the third.
The killing of Arrigoni, a fierce critic of Israel who had reported from Gaza during Operation Cast Lead and called Israel "one of the worst apartheid regimes in the world", is an escalation in the rivalry between Hamas and Jihadist and Salafist groups. Hamas is trying to maintain a semblance of control in Gaza and allows international groups to operate there.