Tunisia’s prime minister, Mohamed Ghannouchi, has assumed the role of interim president and called for a return to order after weeks of violent protests culminated in the 23-year ruler, Zine al-Abidine Ben Al, being driven from the country Friday. Ghannouchi has called for calm and promised early elections, but dissidents, many of them members of the young, restless generation sending shivers down the spines of authoritarians across the Arab world, have promised to return to the streets Saturday. "Tomorrow we will be back on the streets, in Martyrs Square, to continue this civil disobedience until... the regime is gone,” said one protester, whose brother was killed in the upheaval. Ghannouchi promised to restore security to the streets, by force if necessary. "I salute the fact that groups of young people have got together to defend their neighborhoods, but we can assure them we will reinforce their security," he said ominously.