WASHINGTON (AP) -- The Obama administration froze assets of the Libyan government, leader Moammar Gadhafi and four of his children, just hours after it closed the U.S. Embassy in Tripoli and evacuated its remaining staff. 

U.S. officials said announcements of the steps were withheld until Americans wishing to leave the country had departed as they feared Gadhafi might retaliate amid worsening violence in the North African country.

The measures announced Friday ended days of cautious U.S. condemnation of Gadhafi that had been driven by concerns for the safety of U.S. citizens in Libya. They struck directly at his family, which is believed to have amassed great wealth over his four decades in power.

President Barack Obama accused the Gadhafi regime of violating "human rights, brutalization of its people and outrageous threats.'' In a statement issued by the White House, the president said "Gadhafi, his government and close associates have taken extreme measures against the people of Libya, including by using weapons of war, mercenaries and wanton violence against unarmed civilians.''

"I further find that there is a serious risk that Libyan state assets will be misappropriated by Gadhafi, members of his government, members of his family, or his close associates if those assets are not protected,'' Obama said.

"By any measure, Moammar Gadhafi's government has violated international norms and common decency and must be held accountable,'' the statement said. He added that the instability in Libya constituted an ``unusual and extraordinary threat'' to U.S. national security and foreign policy.

As Obama's statement was released, the Treasury Department identified the initial subjects of the sanctions: three of Gadhafi's sons -- heir apparent Seif al-Islam, Khamis and Muatassim -- and a daughter, Aisha. The presidential order also directs the secretaries of state and treasury to identify other individuals who are senior officials of the Libyan government, children of Gadhafi and others involved in the violence.

Stuart Levey, undersecretary for terrorism at the Treasury Department, said officials believe ``substantial sums of money'' will be frozen under the order. He declined to give an estimate.

The sharper U.S. tone and pledges of tough action came after American diplomatic personnel were evacuated from the capital of Tripoli aboard a chartered ferry and a chartered airplane, escorting them away from the violence to Malta and Turkey. As they left, fighting raged on in Tripoli and elsewhere in Libya as Gadhafi vowed to crush the rebellion that now controls large parts of the country.

With U.S. diplomats and others out of harm's way, the administration moved swiftly. Shortly after the chartered plane left Libyan airspace, White House spokesman Jay Carney said the U.S. had been constrained in moving against Gadhafi and his loyalists due to concerns over the safety of Americans but was now ready to bring more pressure on the government to halt its attacks on opponents.   

"It's clear that Col. Gadhafi has lost the confidence of his people,'' Carney told reporters. 

"He is overseeing the brutal treatment of his people, the fatal violence against his own people and his legitimacy has been reduced to zero in the eyes of his people.''

Carney said sanctions would "make it clear that the regime has to stop its abuses, it has to stop the bloodshed.'' International officials say thousands may be dead.   

The hesitancy to outline a broader range of sanctions may reflect in part the administration's skepticism that it had few options to influence Gadhafi and more particularly to assess a successor. The 68-year-old leader has had a rocky relationship with the West, and American officials are worried about his unpredictability as he desperately seeks to maintain his four-decade grip on power.

U.S. military action is considered unlikely, although the Obama administration has not ruled out participation in an internationally administered protective no-fly zone.

Carney said some sanctions would be unilateral, and others would be coordinated with international allies and the United Nations, whose chief, Ban Ki-moon, was invited to Washington for Monday talks with Obama. Carney cited U.N. negotiations on a possible weapons embargo.