The Prime Minister's comments come as 27 EU heads of state are meeting in Brussels.
Bomb detonated inside the mosque in early hours of Wednesday morning.
The Tunisian prime minister said IS was looking to create an emirate in Tunisia.
The town is a hub for illegal trafficking between Libya and Tunisia.
In Libya Daesh has grown from a force of 3,000 fighters to 6,500 in three months.
Italian intelligence officials said they were working to secure the pair's release.
The Italian Foreign Ministry has said it informed the pair's families of their deaths.
Jurgen Todenhofer said disagreements between President Bashar al-Assad and opposition sparked the conflict.
Arms dealers using Facebook to sell a wide range of weapons to Hamas, Kurdish rebels, Isis and other Jihadists.
Interviews with former Caliphate cubs reveal the extent of the abuse in Libya.
Benghazi has seen some of the worst violence in the conflict that has plagued Libya.
A security official in the town said 19 had been killed in overnight clashes.
IS carrying out forced recruitment drive and using child soldiers.
Chouchane is believed to have planned the deadly Sousse beach massacre which killed 30 Britons.
In post-Gaddafi Libya power plays between revolutionary militias have led to a civil war.
Drawings by 11 and 10 year olds in Benghazi show how they view their war-torn city.
Libya has also seen an influx of foreign fighters, a top intelligence official has said.
Pictures purport to show three 'spies' executed by by group in its Libyan stronghold.
The Islamic State is enticing new recruits to enlist as foot soldiers from Africa's most impoverished countries.
Commanders are said to be concerned that RAF pilots are ill-equipped for air-to-air combat.
A team of six RAF officers and MI6 agents are understood to have secretly met in eastern city of Tobruk.
Egypt went on to win the friendly match in Aswan 2-0.