Hamas blamed Israel for the killing of its "commander" Mohammed al-Zawari, an aviation engineer who worked on the development of unmanned aerial vehicles, and vowed to take revenge.
Zawari, 49, had been in Tunisia only a few days when he was shot dead outside his home by multiple gunshots while in his car near Sfax, 270km southeast of Tunis, on Thursday.
Television footage aired on local media showed a black Volkswagen with its windows shot out.
Four rental cars were used in the killing and two handguns and suppressors were seized, Tunisia's interior ministry said.
A judicial spokesman from Sfax, Mourad Tourki, told Tunisian radio Shems FM that eight Tunisian nationals had been arrested in connection with the killing.
|A Hamas poster of Mohammed al-Zawari
One of the suspects is a Tunisian journalist based in Hungary, arrested along with a cameraman. Two other suspects, one of them a Belgian of Moroccan origin, are still at large, Tourki said.
Authorities have not commented on who is suspected of being behind the murder.
Hamas, the Palestinian group that governs the Gaza Strip, confirmed that Zawari had been a member of its military wing for the past 10 years, and spearheaded its drone programme.
A statement said Zawari's work "contributed to the victories" by Hamas during the 2014 Israeli war on Gaza.
The group accused Israel of killing the aviation engineer through its network of spies.
"The assassination of the commander Mohammed al-Zawari in Tunisia is a reminder for all Arab and Muslim nations that the Zionist enemy and its agents are roaming free in the region, playing their dirty roles, and it is time for this cowardly treacherous hand to be cut," Hamas' Qassam Brigades said in a statement.
It published a poster on Twitter showing Zawari with an unmanned drone. The poster bore the logo of Hamas' armed wing and referred to Zawari as a commander.
"The assassination is an aggression against the group and the enemy should know that the blood of this great commander will not be wasted," it said.
Israeli Minister Tzachi Hanegbi, a confidant of Prime Minister Benjamin Netanyahu, told Israeli Channel One: "I hope this issue will not be ascribed to us, that it is not connected to us and that none of those people arrested are our allies."
Tunisia's Islamist Ennahdha movement has called for an investigation into the killing, which it said posed a threat to the country's stability.
Israeli forces were responsible for the 1988 killing of senior Palestinian commander Abu Jihad, whose real name was Khalil al-Wazir, at his home in Tunis, Tunisia.
Wazir was the deputy of then Palestinian chief Yasser Arafat.
Mossad is also believed to have been behind the 2010 murder of top Hamas commander Mahmud al-Mabhuh in a Dubai hotel.
Source: Al Jazeera News