TUNIS - Tunisia, whose revolution convulsed the Arab world, ousted its second leader in less than two months Sunday, as the euphoria triggered by the uprising in January began to give way to the realization that achieving meaningful reforms may prove tougher than toppling dictators.

Tunisian Prime Minister Mohammed Ghannoushi announced in a televised address Sunday that he was stepping down after days of violent clashes between police and protesters in the capital, Tunis, that left three demonstrators dead.

Ghannoushi had taken charge after mass demonstrations forced the resignation of longtime dictator Zine el-Abidine Ben Ali, whose flight into exile Jan. 14 inspired copycat revolts in Egypt and Libya and protest movements in Bahrain, Yemen, Algeria, Jordan and Iraq.

But Tunisians, complaining that the prime minister was too close to the old regime and lacked commitment to the reforms he had promised, had taken to the streets again, this time more rowdily, hurling rocks at shops as well as police as they vented their frustration at the slow pace of change.

The revolutionary fervor unleashed across the region in the wake of Tunisia's revolt shows no sign of abating, and on Sunday it spread to two countries in the oil-rich Persian Gulf that had hitherto seemed relatively immune to the turmoil elsewhere.

In the tightly controlled kingdom of Saudi Arabia, a group of 119 academics and activists called for sweeping political reforms in a statement posted on Saudi Web sites. On Twitter and Facebook, activists called for demonstrations March 11 and 20 to demand reforms, echoing the "Day of Rage" dates set by activists elsewhere in the region that have in some places triggered full-scale uprisings.

The statement by the academics did not call for the overthrow of the Saudi monarchy or challenge the rule of the ailing and aging King Abdullah, whose promises to reform the highly restrictive country have stalled amid squabbles over who among his relatives should succeed him.

But it did call for the replacement of the current system with a constitutional monarchy that would dramatically reduce the hereditary powers of the royal family, raising the specter of unrest spreading to the world's largest oil producer.

And in placid Oman, a sleepy, palm-fringed beach nation on the Arabian Sea where the sultan has long been regarded as one of the region's more benevolent rulers, two people were killed in clashes between police and demonstrators in the town of Sohar, 120 miles northwest of the capital, Muscat. Oman's state-run news agency said protesters demanding political reforms, jobs and higher wages set fire to the governor's residence and burned a police station, houses and cars.

Even in Lebanon, which has no government to rebel against because of disputes among the country's feuding political factions, demonstrators took to the streets to demand the overthrow of the sectarian system that has defined and divided the volatile country for seven decades.

Yet even as the tumult spreads and intensifies, some of the heady optimism that accompanied the initial uprisings in Tunisia and Egypt is starting to fade.

Tensions are building in the tiny island nation of Bahrain, where two weeks of protests originally aimed not at overturning the regime but at securing constitutional reforms have drawn only trifling concessions from King Hamad bin Isa al-Khalifa.