BENGHAZI, LIBYA - Col. Moammar Gaddafi faced fresh setbacks domestically and internationally early Sunday with opposition forces in eastern Libya preparing to dispatch a rebel force to his stronghold in Tripoli and the United Nation's imposing military and financial sanctions while raising the specter that the isolated leader could face charges for crimes against humanity.

Even as the opposition consolidated its grip on the country's second city, Benghazi, a top anti-Gaddafi leader, Brig. Gen. Ahmed Gatrani, said a small force comprising army defectors and rebels has already reached the outskirts of the capital. An attempt to oust Gaddafi in Tripoli on Friday was crushed by pro-regime paramilitaries and soldiers firing indiscriminately at protesters on the streets.

It happened as the wave of civil revolts of recent weeks continued to convulse the Middle East, with even Tunisia and Egypt, two nations where protesters succeeded in ousting longtime authoritarian rulers, seeing heated protests on Saturday that led to violent military crackdowns. In Oman on Sunday, two people were killed in protests, Reuters reported, as police fired tear gas and cordoned off protesters demonstrating for a second day in the city of Sohar.

But the focus remained on the upheaval in Libya. "We are trying to organize people who will sacrifice their lives to free Tripoli from the dictator," said Gatrani, who heads the military committee now in charge of the army in Benghazi, 600 miles east of the capital and the first major city to fall under opposition control. But, he cautioned: "Entering Tripoli is not easy. Anyone trying will be shot."

The prospect of a rebel army marching on the capital to confront loyalist members of the same army raised the specter of outright civil war in a country already violently polarized between supporters and opponents of the regime. In another sign of the deepening division, Mustafa Abdel Jalil, the former justice minister who recently defected, announced the formation of an "interim government'' to lead the eastern regions under rebel control.

Secretary of State Hilary Rodham Clinton before departing for Geneva for a meeting of the U.N. Human Rights Council repeated her call for Gaddafi to leave. "We think he must go as soon as possible without further violence and bloodshed," Clinton said. "There will be accountability for the crimes against humanity and war crimes" committed in recent days in a crackdown against protesters. Delivering a message directly to Gaddafi and his inner circle, Clinton said, "You will be held accountable for actions that have been taken against your people."

Clinton praised the vote of the U.N. Security Council on Saturday and said the action will allow the United States and its allies to move more aggressively in several ways, including providing humanitarian relief to Libyans. She called on neighboring countries to help the international community in preventing the movement of mercenaries and other fighters into Libya to prop up the Gaddafi regime. The U.N. meeting Monday is expected to explore ways to coordinate sanctions against the Libyan government and respond to the growing humanitarian crisis in the region.

With eastern Libya largely under opposition control, the struggle for the west remained paramount. Towns near the western border with Tunisia have fallen under opposition control, with Gaddafi loyalists, if not staging a full counterattack, battling to slow the sandwiching of government forces to zones around Tripoli.

In interviews with news agencies, Gaddafi's son, Saif al-Islam, alternately suggested the government was willing to negotiate with protesters while warning that the nation was falling into civil war. "The unrest will break up the country just as in Afghanistan," he told broadcaster Al Arabiya.

Pro-Gaddafi forces still maintained control of the western border with Tunisia and had set up approximately 20 checkpoints on the road to Tripoli, with western towns taken over by the opposition in recent days in danger of being cut off from food, medical supplies and fuel.

In the key cities of Sabratha and Zawiya, west of Tripoli, major tribal families appeared to be controlling the town centers but were still engaged in night battles with government forces on the outskirts of town.

"There is no food in the shops, there is no rice, no sugar, no bread, no flour. All you can find there is canned foods," said Mohammed Siyam, 24, an Egyptian laborer who arrived at the Tunisian border Sunday morning after fleeing Subratha.