The EU has blamed Isis for the attack at a museum in Tunisia that left 19 people dead, including 17 foreign tourists.
European Union foreign policy chief Federica Mogherini said in a statement: "With the attack that has struck Tunis today, the Daesh terrorist organisation is once again targeting the countries and peoples of the Mediterranean region."
"This strengthens our determination to cooperate more closely with our partners to confront the terrorist threat," she said.
"The EU is determined to mobilise all the tools it has to fully support Tunisia in the fight against terrorism and reforming the security sector."
Tunisia has struggled with violence by armed groups in recent years, including some linked to Isis in Iraq.
A researcher at the Quilliam think tank has tweeted a message from a prominent Isil supporter that today's attack is the start of a wave of terrorism in Tunisia.
Thousands of Tunisians are believed to have left the country to fight for jihadist groups in Syria and Iraq.