BENGHAZI, Libya – Moammar Gadhafi found himself on Saturday even more isolated in his last major stronghold of Tripoli, as a former top aide declared he was forming a national opposition government and President Obama said the Libyan dictator should leave “now.”

The United Nations Security Council, meanwhile, unanimously approved sanctions aimed at forcing Gadhafi to halt brutal onslaughts that he has unleashed in a bid to crush an 11-day-old insurrection that has left all of eastern Libya and other parts of the country under rebel control and has left hundreds, if not thousands, dead.

The Security Council, after a day of discussions behind closed doors and consultations with home capitals, agreed to freeze the assets of Gadhafi, his four sons and one daughter, and to ban travel by the whole family plus 10 close associates. Possible war crimes charges would be referred to the International Criminal Court.

Obama, in a telephone call with German Chancellor Angela Merkel, “stated that when a leader’s only means of staying in power is to use mass violence against his own people, he has lost the legitimacy to rule and needs to do what is right for his country by leaving now,” the White House said in an official readout of the call between the leaders.

Obama also has frozen the U.S. assets of Gadhafi, his family and top officials and shuttered the U.S. Embassy in Tripoli.

Until Saturday, Obama had refrained calling directly for Gadhafi to step down, saying it was for the Libyan people to decide. Secretary of State Hillary Clinton said in a statement Saturday that Libyans “have made themselves clear” about their wishes.

The harsher language follows the evacuation of most U.S. citizens from Libya, and days of accounts of Gadhafi’s forces shooting into crowds and homes, flying in African mercenaries, paying civilians to turn against one another, taking hostages and ambushing people by hiding in civilian cars, taxis and ambulances.

Gadhafi’s former justice minister, Mustafa Mohamed Abud Ajleil, was announced to lead the opposition’s interim government, to be based in eastern Libya in the country’s second-largest city, Benghazi, which Gadhafi no longer controls. Organizers said the plan was for the temporary government to serve until Gadhafi could be deposed and free elections held with Tripoli as the permanent capital.

Former Libyan Interior Minister Abdul Fattah Younis, who resigned and defected to the opposition on Feb. 20, told the Al Jazeera satellite channel that Gadhafi’s forces control only Tripoli and “a few other towns.”

“That’s why I urge the Libyan people that there is no going back. Going back is impossible,” he said.

In the latest high-level defection to rock the regime, the commander of the Libyan military’s special operations forces also called on his men to join the insurrection against Gadhafi.

“I place all of my resolve and capabilities at the service of the youth revolution,” Gen. Abdul Salam Mahmood al-Hassi declared on Al Jazeera, and he urged other special forces to join to “protect the lives of the Libyan people and their property.”

The online edition of the Quryna newspaper, formerly run by the state but now in the hands of the rebels, reported Saturday that Ajleil said that Gadhafi alone bore responsibility “for the crimes that have occurred” in Libya, that the country must stay unified and that Gadhafi’s tribe, the Gadhadhfa, would not face blame.

Gadhafi’s son, Seif al-Islam, was quoted by Reuters as telling invited foreign journalists that Tripoli was calm and free of violence. “Everything is peaceful,” the report quoted him as saying, and “peace is coming back to our country.”

“It’s getting worse,” said one Tripoli man, interviewed by cell phone on Saturday, whose report could not be independently confirmed.

The man, who asked his name be withheld to protect his security, said that Gadhafi militias had set up six checkpoints along a 1-kilometer stretch near his home. “There is no shooting. But there are a lot of Land Cruisers with militia in them. They are wearing civilian clothes and are armed.”

Four helicopter gunships made repeated runs from Gadhafi’s palace, the Bab Azaziya, in the center of Tripoli, out to a military base to the west, raising fears that an assault was being planned against rebel-held Zawiya, the country’s fourth-largest city, about 20 miles west of Tripoli, another resident said.

Residents reached in Tripoli said the capital of some 2 million people was largely quiet, with Gadhafi’s militiamen erecting additional roadblocks and tanks parked at major intersections.

Many pro-Gadhafi militiamen traded their uniforms for civilian clothes and were rolling through the streets in civilian cars to catch unawares any anti-regime protesters who might try to start new demonstrations, they said.

A woman said that regime supporters were cleaning up bodies and debris.

Residents reached by telephone said they were running out of food, international relief groups considered it too dangerous to begin a major relief effort, and there were fears that Gadhafi was preparing to unleash new assaults to extend his control to rebellious areas outside of Tripoli.

“Now it’s very difficult with food. Maybe between three or four days, there will be no food,” said Essam, a resident of Tajura, a town about 15 miles southeast of Tripoli. His last name is being withheld for his safety. “Everyone is in their homes. It is very difficult.”

He said militiamen loyal to Gadhafi were lurking in the streets a day after thousands of residents tried to march into Tripoli to join tens of thousands of protesters who were met with gunfire and beatings by pro-Gadhafi forces backed by tanks.

In Misrata, about 100 miles east of Tripoli, heavy fighting raged around the sprawling headquarters of the Khamis Brigade, a military unit named after one of the Libyan dictator’s sons, said residents reached by telephone.

“We have surrounded it,” said one of the protesters, Mohammad el-Habab, referring to an air force school inside the complex. “We heard the military using its heavy weapons against the peoples’ lighter weapons.”

At one point, he said, a commander came out of the school and agreed to negotiate, having run out of food and water. The rebels said they would put the commander on trial if he agreed to surrender his weapons, which he did. Habab said that despite the heavy fighting he knew of no deaths there.

Rumors swirled around Benghazi on Saturday that Gadhafi’s son, Saif al Islam, was willing to negotiate a truce with leaders of the insurrection in Misrata and Zawiya.

In Tajura, another man reached on his cell phone said there had been no new assaults by Gadhafi forces. He said the relative quiet allowed him to tend to his brother, who was shot in a leg by Gadhafi forces a day earlier.

Meanwhile, evacuations of foreign nationals from Libya continued.

In Paris, the French Foreign Ministry announced that a French Air Force flight flew 122 people, including 28 French citizens and 94 foreigners, out of Libya on Saturday.

The British Foreign Office said a frigate, HMS Cumberland, arrived in the Maltese port of Valletta from Benghazi before dawn Saturday, carrying 207 passengers, including 68 British citizens.