In this August 29, 2008 file photo, international activist Vittorio Utmpio Arrigoni, from Italy, holds his passport during a protest against the Israeli siege on Gaza, in Gaza City. (Hatem Moussa/AP)

A pro-Palestinian activist from Italy who had been abducted by an al-Qaeda-inspired group in the Gaza Strip was found strangled to death early Friday, the first such slaying of a foreigner in the coastal territory ruled by the militant group Hamas, which called it “a crime.”

The body of Vittorio Arrigoni, 36, was discovered by Hamas security forces in an empty house in Gaza City a day after he had been seized, officials said. Arrigoni had been strangled with a plastic handcuff strip, said Khalil Abu Shammala, director of Al-Dameer Association for Human Rights, who went to the scene with security officials. He said Arrigoni’s head was bloodied, apparently from being beaten before he was killed.

“It seems that he was subjected to torture,” Abu Shammala said in a telephone interview. “I have seen many bodies during the intifada and after assassinations by Israeli soldiers, but I was totally shocked when I saw the way they killed him.”

An extremist group calling itself al-Tawhid wal-Jihad, or Monotheism and Holy War, had asserted responsibility for the abduction. The group’s leader, Sheik Abu Walid al-Maqdisi, was arrested last month by Hamas. The group, which affiliates itself with the Salafist branch of Islam, threatened to kill Arrigoni unless Maqdisi and other imprisoned members of the organization were freed.

A YouTube clip posted Thursday by the abductors showed Arrigoni blindfolded and bloodied near his right eye, his head held up to the camera by one of his captors grabbing his hair.

An accompanying text said: “The Italian hostage entered our land only to spread corruption.” It described Italy, which is predominantly Catholic and the home of Vatican City, as “the infidel state.”

The kidnappers had set a deadline of 5 p.m. local time Friday for their leaders’ release. But medical findings indicated that Arrigoni was slain hours before that, in the early morning, apparently when his captors learned that Hamas police were preparing to close in on their hideout, security officials said.

A member of the extremist group who had been arrested and interrogated disclosed the abductors’ location, an Interior Ministry spokesman said.

The spokesman, Ehab al-Ghussein, denounced the killing as “a crime that does not reflect the values, morals, religion and customs” of the people of Gaza.

Arrigoni arrived in Gaza in 2008 on a boat carrying humanitarian supplies that Israel allowed through despite its naval blockade on Gaza. He last returned to the area a year ago, through the Rafah crossing on the Egyptian border.

He was active in the International Solidarity Movement, a group that documents and Israeli military actions in the West Bank and Gaza Strip and tries to disrupt them using nonviolent methods. He accompanied fishermen challenging Israeli-imposed boating restrictions off Gaza and escorted farmers entering their land in an off-limits zone along the border that was created by Israel in response to militant attacks and enforced by the Israeli army.

Salafism is inspired by Wahhabi Islam, the fundamentalist version of Islam that is dominant in Saudi Arabia. Al-Tawhid wal-Jihad incorporates Salafi religious beliefs into armed struggle.

The group, along with other radical Salafist factions, has challenged Hamas in Gaza, denouncing it for halting rocket attacks against Israel under cease-fire arrangements and for having participated in governments with the secular Fatah movement as part of the Palestinian Authority.

The Salafis have accused Hamas of failing to strictly enforce Islamic law and have attacked Internet cafes, which they view as purveyors of decadent Western culture.

More than a dozen foreign correspondents and aid workers were abducted in Gaza before Hamas seized control of the territory in June 2007, but all were released unharmed, usually within hours or days. The last to be kidnapped was Alan Johnston, a correspondent for the BBC, who was held for 114 days by militant captors before being freed under heavy pressure from Hamas shortly after its takeover.