A still image taken from a YouTube video on Thursday purportedly shows blindfolded Italian Vittorio Arrigoni. YouTube Via Reuters

GAZA CITY, Palestinian Territories - A radical Islamist group hanged an Italian activist on Friday hours after kidnapping him in Gaza, Hamas said, as Rome denounced the "barbaric murder".

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The pro-Palestinian activist was found hanged in a house north of Gaza City, the ruling Hamas government said.

"The government media office denounces the criminal kidnapping and murder of an Italian solidarity activist ... who was found by security hanging in an abandoned house in northern Gaza," it said.

Hamas said that two suspected kidnappers were arrested, and security officials were looking for accomplices.

The pro-Palestinian International Solidarity Movement named the activist as 36-year-old Vittorio Arrigoni, who had been living in the Gaza Strip for much of the past three years.

In a video posted on YouTube, the kidnappers said that Arrigoni had been taken hostage in order to secure the release of an unspecified number of their members detained by Hamas security forces, including a jihadi leader called Sheikh Hisham al-Suedani.

The kidnappers, who identified themselves as belonging to The Brigade of the Gallant Companion of the Prophet Mohammed bin Muslima, said that they would execute Arrigoni if their demands were not met by 5 pm on Friday.

"If you don't respond quickly to our demands, within 30 hours from 11 am on April 14, we will execute this prisoner," they said.

It was unclear why they killed their hostage before the expiration of the deadline.

Hamas government spokesman Ihab al-Ghoussein branded the murder a "heinous crime which has nothing to do with our values, our religion, our customs and traditions" and said that "the other members of the group will be hunted down and the law will be applied".

"When news of the kidnapping of Italian activist Vittorio Arrigoni became known, security services went on general alert, and the investigation has led to a member of the group who gave away the other members and showed the place where the activist was kept," he said in a statement read on television.

"The security services moved competently and quickly and found the body of the hostage who had been killed several hours earlier in an atrocious way according to a forensic doctor."

In Rome, the Italian foreign ministry denounced "in the strongest manner the act of vile and senseless violence committed by extremists who are indifferent to the value of human life".

Agence France-Presse