Prime Minister Benjamin Netanyahu said on Saturday that Israel had learned of "concrete threats" of terror attacks against Jewish or Israeli targets in the North African country, prompting a quick denial from Tunis.
Interior Minister Najem Gharsalli told journalists in the holiday resort of Djerba, which hosts an annual pilgrimage to the Ghriba, Africa's oldest synagogue, that security forces and the army were ready.
"They are here and the security plan is in place" for the May 6-7 pilgrimage, he said.
"Tunisia is a safe country and Djerba too is a safe city. Visitors from the world over are welcome," Gharsalli said.
"What I am saying now is a response to many who cast doubt over Tunisia's security and its capacity to secure celebrations," he added.
A statement from Netanyahu's office late on Saturday said: "Information indicates that there are plans for terrorist attacks against Israelis or Jews in Tunisia" connected to the pilgrimage.
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Thousands of pilgrims visit the tombs of famous rabbis for the Lag BaOmer Jewish Festival, including on Djerba island, where one of the last Jewish communities in the Arab world still lives.
Beginning 33 days after the start of the Jewish Passover festival, the Ghriba pilgrimage used to attract thousands of pilgrims from France and Israel and other tourists.
But their number fell dramatically after an April 2002 bombing blamed on Al-Qaeda that killed 21 people.
According to legend, the Ghriba synagogue was founded in 586 BC by Jews fleeing the destruction of the Temple of Solomon in Jerusalem.
Tunisian Jews now number around 1,500, compared with an estimated 100,000 when Tunisia gained independence in 1956.
The Israeli Counter-Terrorism Bureau said it was advising people against visiting Tunisia in view of the "threats".
But Gharsalli insisted that Tunisia can protect visitors "better than any other country".
The authorities have been trying to reassure foreign visitors they will be safe since 21 tourists were killed in a jihadist attack on the Bardo National Museum in Tunis in March.