Ghannouchi, 69, has been a major irritant to Tunisians behind the so-called "Jasmine Revolution" -- weeks of public upheaval that drove longtime autocratic President Zine El Abidine Ben Ali from power last month.
Even though Ben Ali fled to Saudi Arabia on Jan. 14, Ghannouchi -- who served for 11 years as his prime minister -- had promised to stay on to guide the country until elections this summer.
Ghannouchi's announcement on state TV and radio came a day after officials said at least four people had died in recent days in the capital during clashes between stone-throwing protesters and police.
