The official Tunisian news agency says a man has blown himself up in front of a hotel in a Mediterranean resort town.
The TAP news agency on Wednesday said the man, wearing a belt of explosives, was killed. No one else was hurt in the explosion in the town of Sousse, about 150km south of the capital, Tunis.
Sousse is a frequent destination for tourists.
Also on Tuesday, Tunisian police said they captured a man who tried to blow himself up at the tomb of Habib Bourguiba, a former president, in the town of Monastir.
"The two suicide bombers are radical Islamist jihadists. They are Tunisians, but they had been in a neighbouring country," said Interior Ministry spokesman Mohammed Ali Aroui, without specifying the country.
The first bomber tried to enter the Riadh Palms Hotel with a suitcase, and was turned away. He then ran onto the beach and blew himself up, a security source said.
The bombing is bad news for the vital tourism industry in Tunisia, which attracted 5.8 million mostly European visitors to its Mediterranean beaches and desert tours in 2012.
"We don't know the consequences right now ... Whatever happens it will be negative because this is the first time they attack a hotel," said Mohamed Ali Toumi, head of Tunisia's federation of travel agencies.
Security stepped up
Police tightened security in the capital Tunis and sealed off the nearby village of Sidi Bou Said, which is popular with tourists. Hundreds of police deployed in other resorts such as Hammamet and Djerba.
Rached Ghannouchi, leader of Ennahda Party, which governs in coalition with two secular parties, condemned attacks on tourists, which he said targeted Tunisia's political transition.
"Whoever tried to assault the tourists and the tomb of President Bourguiba are criminals who want to destroy the economy and democratic transition in Tunisia," he said. "They will not succeed, thanks to the vigilance of our security and our army and our unity against terrorism."
The attack comes a day after Tunisia's army launched an operation in the central Sidi Bouzid region to track down armed men who had killed six policemen in the area, the defence ministry said.
Tunisia has been battling unrest since the overthrow of Zine El Abidine Ben Ali's regime in 2011, and has seen the rise of self-declared jihadist movements.