Isis beheaded Khaled Al-Asaad in a public square in Palmyra in front of dozens of onlookers, the Syrian Observatory for Human Rights (SOHR) said on its website on Tuesday.
The 82-year-old expert was the former director of the city's world-famous archaeological site and his body was hung from a pillar after he was decapitated.
“The beheading of Khaled Al-Asaad is a gesture that provokes horror,” Franceschini said in a statement released on Wednesday.
“The barbaric violence towards a man who dedicated his life to the cultural heritage of his own country is the very rejection of civilization.”
“This horrible act cannot pass without a response. The Declaration of Milan endorsed at Expo by nearly 90 countries is the first step, now we need a major commitment from the international community to defend culture and people in areas of crisis.”
The news of the archaeologist's death was initially given by Syrian Antiquities and Museums Director, Maamoun Abdulkarim, to Syria's state-run news agency, Sana.
Al-Asaad is reported to have been arrested a month ago and interrogated by members of Isis seeking information on where Roman artefacts may have been hidden before Isis occupied the ancient city in May.
He had been director of the Palmyra archaeological site for 40 years until his retirement in 2003. Sana reports that he had continued to work as an expert after his retirement for the Antiquities and Museums Department.
He had also worked with US, French, German and Swiss archaeological missions on excavations and research in Palmyra's 2,000-year-old ruins, which is a Unesco World Heritage site that includes Roman tombs and the Temple.