An unknown radical Muslim group on Thursday said it kidnapped a European activist in the Gaza Strip and demanded Hamas authorities to free members of the Salafi group.

A file photo taken on June 3, 2010 shows Italian peace activist Vittorio Utmpio Arrigoni waving a Palestinian flag aboard a ship during an activity calling for lifting the Israeli siege on Gaza, at Gaza seaport. An unknown radical Muslim group on Thursday said it kidnapped Arrigoni, 36, in the Gaza Strip and demanded Hamas authorities to free members of the Salafi group. [Ashraf Mohammed/Xinhua]

The group released a video showing the hostage blindfolded and called on Hamas to release the leader of Al-Tawheed and Al-Jihad group within 30 hours starting from 09:00 am GMT Thursday.

It threatened to execute the hostage if Hamas did not release the prisoners.

The video said the hostage was Italian, and identified his first name as "Victor."

It could not be immediately confirmed if the man was an International Solidarity Movement activist who came to Gaza on the first ships that challenged an Israeli blockade on Gaza in 2008. That activist is known to Gazans as "Victor" and he is an Italian national.

Hamas, which has controlled Gaza since 2007, launched several crackdowns on supporters and members of Salafi groups, which follow more hardliner conception of Islam than Hamas.