TUNIS (REUTERS) - Tunisia arrested 32 militant Islamists, some of them returning from fighting in Syria, who planned "spectacular" attacks, officials said on Saturday.

News of the arrests came one day after a secular-Islamist coalition Cabinet headed by Prime Minister Habib Essid took office.

The new Cabinet faces many challenges, including Islamist groups that emerged after a 2011 uprising to threaten its nascent democracy.

"Counter-terrorism forces foiled plots to carry out spectacular attacks against vital installations, including the Interior Ministry, security stations and civilian buildings in the capital Tunis," said Mohammed Ali Aroui, a spokesman for the Interior Ministry.

"During the past three days, we arrested 32 terrorists from this group planning to attack targets in Tunis and other cities," he said, adding that the group included "several terrorists returned from fighting in Syria."

Since a 2011 uprising in Tunisia toppled the regime of Zine El Abidine Ben Ali, the country has become a major source of militant fighters travelling to Syria.

With an economy heavily reliant on foreign tourism, Tunisia has been cracking down on Islamist militants.

"Our priority will be to strengthen measures to combat extremism and strengthen security capabilities to confront terrorism and the protection of the democratic transition," Essid said this week.

The number of Tunisians fighting in Syria has been estimated at about 3,000.

A few hundred have returned to Tunisia and many have been tracked down and arrested.

Aroui said special forces are pursuing other militants in the southern city of Gafsa led by an Islamist named Mourad Gaesseli.

He did not give details about the identity of this group.

Ansar al-Sharia, which the United States lists as a foreign terrorist organisation, was among the most hardline movements calling for an Islamic state to emerge since Tunisia's 2011 uprising.

It has claimed responsibility for attacks in Libya in recent months.