A radical group has kidnapped an Italian activist in Gaza and threatened to kill him within hours, unless Hamas government releases its detained members.

Foreign aid workers in the enclave named the man as Vittorio Arrigoni and said he was an activist with a pro-Palestinian group called the International Solidarity Movement (ISM), who was also working as a journalist and writer.

In a video posted on YouTube on Thursday, the Salafist group said it had taken him hostage in order to secure the release of an unspecified number of their members who had been arrested by the security forces in the Hamas-ruled Gaza Strip.

It said it would execute him if their demands were not met by 5:00 pm (1400 GMT) on Friday.

"We kidnapped the Italian prisoner Vittorio and we call on the Haniya government … to release all our prisoners," it said, referring to Hamas premier Ismail Haniya and naming an imprisoned jihadi leader called Sheikh Hisham al-Suedani.

"If you don’t respond quickly to our demands, within 30 hours from 11:00 am (0800 GMT) on April 14, we will execute this prisoner," it said.

Arrigoni was shown blindfolded in the 3-minute clip with blood around his right eye and a hand can be seen pulling his head up by his hair to face the camera.

A spokesman for the Hamas interior ministry in Gaza City said it was investigating the abduction.

In Rome, the Italian foreign ministry said it had been informed by its consulate in Jerusalem of Arrigoni’s kidnap and had "already taken the opportune steps to intervene to protect him."

A statement added that Foreign Minister Franco Frattini was following the matter closely and that a crisis unit at the ministry was in contact with Arrigoni’s family.

The Arabic text that accompanied the footage of Arrigoni also said "the Italian hostage entered our land only to spread corruption" and it described Italy as "the infidel state".

A statement released by Palestinian President Mahmoud Abbas in the West Bank called for Arrigoni’s "immediate and unconditional release" and said it was counterproductive.

"This action does not serve the just cause of the Palestinian people and harms it," Abbas’s statement said.

Arrigoni is the first foreign national to be abducted in the Gaza Strip since BBC journalist Alan Johnston, who was held for 114 days by a group named the Army of Islam. He was released in 2007.

(Al Jazeera)