The Tunisian capital was hit by an attack on its most prestigious museum, leaving 19 people dead, including two Tunisians and 17 foreign tourists, and over 40 injured.
Gunmen stormed the Bardo Museum, world famous for its large collection of Roman mosaics, and started shooting at tourists, killing several. Two gunmen were killed by police.
President Beji Caid Essebsi said the country was "in a war with terror".
"These monstrous minorities do not frighten us," he said in remarks broadcast on national TV. "We will resist them until the deepest end without mercy.
"Democracy will win and it will survive."
Prime Minister Habib Essid said: "It is a critical moment in our history, and a defining moment for our future."