Thousands decried the growing violence in Tunisian politics during a protest in the capital Monday, warning that the nation's nascent democracy is at risk almost exactly a year after it held historic elections.

The march in Tunis came four days after the death of a union leader during a protest that turned violent.

Nine people were injured in the small protest in Tataouine, in the south, and the union leader died of what the Interior Ministry said was a heart attack. A banner at the head of the march bore an image of the face of the union leader, baptized a "martyr for democracy."

Opposition party offices in Tunisia also have been attacked and, in the most brazen violence, thousands of protesters stormed the U.S. Embassy compound a month ago. Some of the protesters tore down the American flag and looted the nearby American school. On its website, the U.S. Embassy says the security situation remains unpredictable.

Some 4,000 people concerned over the degenerating climate marched down the main avenue of the capital during Monday's demonstration. Among them was former Central Bank Governor Mustapha Kamel Nabli, who called for "peace and concord" in this "critical period."

Tunisians ousted dictator Zine El Abidine Ben Ali in January 2011, triggering protests against autocrats in other Arab countries in what became known as the Arab Spring.

On Tuesday, Tunisians mark the first anniversary of the first post-Ben Ali elections, which gave the moderate Islamist party Ennahda the leading role in a government coalition. However, the climate is tense as ultra-conservative Muslims become increasingly visible and persistent social unrest, often over economic issues, fails to ease.

Monday's march "is a national day against violence to save the democratic transition from the dangers threatening it," said the spokesman for the small centrist party Nida' Tounes, or the Call of Tunisia.