Tunisian police arrested an imam after he delivered a sermon described as "insubordinate," the Interior Ministry said Wednesday, in the first high-profile arrest since the government began taking a harder line toward religious conservatives.

After facing accusations that it has been lax in enforcing the law, Tunisia's moderate Islamist ruling party has been increasingly tough on ultraconservative Muslims known as salafis, some of whom have engaged in violence in in an effort to promote greater piety in society.

On Monday, six men were convicted and sentenced to five years in prison for burning down a shrine to a Muslim saint on the outskirts of Tunis last October. Such shrines are seen as heretical by some ultraconservative Muslims.

According to a brief Interior Ministry statement, the preacher was arrested Tuesday after he called some of his congregation at a mosque in central Tunisia's Sidi Bouzid province unbelievers and mentioned the government's hunt for al-Qaida-linked militants near the Algerian border. It did not provide details on what exactly he said.

Imams in Tunisia are not allowed to discuss politics from the pulpit. Describing Muslims as "unbelievers" because they are not sufficiently pious reflects a very hardline approach to the faith.

There has been a rise in ultraconservatism since the overthrow of Tunisia's secular dictatorship in 2011. At least 100 mosques are believed to be headed by hardline preachers promoting jihad in Syria and other countries. Religious Affairs Minister Nourredine Khademi recently announced a new effort to retake control of these dissident mosques.

According to Tunisia's Sufis, practitioners of a mystical form of Islam, some 40 shrines and mausoleums have been destroyed in Tunisia. Religious hardliners have destroyed others in northern Mali, Somalia and other countries.