TUNIS — The authorities in Tunisia have arrested nearly 800 people who were protesting tax increases and other government policies after a series of clashes with the police. The arrests have alarmed observers of Tunisia, the only country to emerge from the turmoil of the Arab Spring with a semblance of a stable democracy.

Although some of those who were arrested were released, the number of detentions drew criticism from human rights groups.

“We’re concerned about the high number of arrests,” Rupert Colville, a spokesman for the United Nations High Commissioner for Human Rights, said Friday in Geneva. “Some 778 people we understand have now been arrested since Monday, and around a third of those arrested were between the ages of 15 and 20.”

He added: “We call on the authorities to ensure that people are not arrested in an arbitrary manner and that all those detained are treated with full respect for their due process rights and are either charged or promptly released.”