ISIS has claimed responsibility for last Friday's assault on theImperial Marhaba hotel in the resort town of Sousse. The gunman, Saif Rezgui, was shot dead by police.
"We will find all those involved, whether it was just logistical support or not," the minister said, flanked by ministers from Britain,France and Germany.
The number of Britons confirmed killed by the Islamist gunman in Friday's attack has risen to 18 from 15 and the final death toll of Britons is likely to increase to around 30 people, a British spokeswoman said.
Thousands of tourists have left Tunisia since Friday's attack, which has shocked a country that relies heavily on tourism for jobs and foreign currency revenues.