Tunisian President Moncef Marzouki's secular party is quitting the coalition government in anger at the dominant Islamist party's handling of the country's worst political crisis since it unleashed the Arab Spring uprisings two years ago.

The move by the Congress for the Republic party threatens to deepen the crisis, prompted by the assassination of an opposition leader last week.

Marzouki was a longtime human rights activist whose ascension to the presidency was seen as a sign of Tunisia's democratic progress after it overthrew a longtime authoritarian president in 2011.

The center-left Congress for the Republic party, which Marzouki founded, said Sunday that it is quitting the coalition government, the state news agency TAP reported. The party had wanted negotiations on a new government.

The coalition government is currently led by the Islamist Ennahda party, which dominated Tunisia's first free elections. Marzouki's party and the secular Ettakatol party also held some government seats.

Fringe violence by radical Islamists has mounted in Tunisia, and secular critics of Ennahda accuse the party of not doing enough to stop the extremists.

The shooting death on Wednesday of opposition leader Chokri Belaid — one of Ennahda's most outspoken critics — sparked nationwide protests and calls for a new government.

The prime minister, an Ennahda member, wants to form a new government of non-political technocrats. But Ennahda party leadership rejects that idea. A crucial party council is meeting Sunday to discuss what to do.

After three days of street violence, the capital Tunis was relatively quiet Sunday, under the watchful eye of riot police.

Professor Khaled Adouani expressed hope Sunday that the government would find a "disciplined" solution to the crisis, noting that a pro-Ennahda rally in Tunis ended peacefully. "We must not in these delicate circumstances think about anything else other than legality," he said.

Musician Imed Amar, however, echoed concern about a divide within Ennahda between moderates and hard-liners. "Things are getting complicated, the disagreements are growing inside the Ennahda itself," the 29-year-old said.