Hamas has blamed the Israeli national intelligence agency Mossad for the assassination of one of its Tunisian members after conducting an 11-month-long investigation.

The Palestinian group said Mohammed al-Zawari, a commander of its armed wing the Qassam Brigades since 2006, was fatally shot outside his home multiple times while in his car near Sfax, 270km southeast of Tunis, on December 15, 2016.

Hamas had set up an investigative committee in the immediate aftermath of the assassination.

Speaking at a press conference in Beirut on Thursday, Mohammed Nazzal, Hamas politburo member, called the Mossad operation a "terrorist act".

"Mossad is officially accused of being behind the assassination, which is not only a terrorist act, but a violation of state sovereignty," he said.

Nazzal also said that it is within their "responsibility to coordinate with Tunisian authorities" on matters relating to the country's national security "to confront the Zionist enemy".

"Tunisia has information regarding the investigation as well, and its national interest and stability is highly important to us," Nazzal said.

"Because the Zionists may repeat its doings once again, and as such we are responsible for Tunisia's security - and we would be for any other Arab state."

According to Hamas, the 49-year-old al-Zawari was an aviation engineer who worked on the development of unmanned aerial vehicles.

The movement credited him with developing the "Ababeel" drones used in the last Israeli offensive on the Gaza Strip in the summer of 2014.

The full investigative report, which is published on Hamas' website, includes details of how the assassination was meticulously planned over three stages in 2015 and involved 12 individuals.

The two men who carried out the assassination had Bosnian passports.

One of the individuals, who went by the name of Chris Smith, had enrolled in the National Engineering School of Tunis - the same university where al-Zawari was studying for his postgraduate degree.

The report said that Smith, who had told the university he wanted to observe drone innovation, had offered al-Zawari a project, allegedly backed by the European Union, to work on. Al-Zawari declined after becoming suspicious of him.

Nazzal said that Hamas has a legal body and that it will present their investigative report to them in order to study possible options to proceed with the findings.

"I assure you that the legal team will examine this," he said. "We will look into the options of bringing forward lawsuits against Israel."