WASHINGTON - As more Libyan towns and cities fell to anti-government forces Wednesday, U.S. President Barack Obama said Washington is preparing "the full range of options" to respond to the ongoing violence in the oil-rich North African state.

MARCH ON TRIPOLI? Libyan protesters shout anti-Kadhafi slogans in the eastern Libyan town of Derna on Wednesday. Residents of Libya's dissident-held east, frenzied by a deadly crackdown by Moamer Kadhafi's crumbling regime, vowed on Thursday to march on the capital Tripoli as a string of towns famous as World War II battlegrounds fell under their control. In a five-minute televised statement from the White House, Obama stressed that Washington preferred to act in concert with other nations and international institutions.

"This is not simply a concern of the United States," he said as Secretary of State Hillary Clinton stood by his side. "The entire world is watching, and we will coordinate our assistance and accountability measures with the international community."

But he also hinted that Washington may consider taking unspecified unilateral action against the regime of Libyan leader Muammar Gaddafi.

"I've …asked my administration to prepare the full range of options that we have to respond to this crisis," he said. "This includes those actions we may take and those we will coordinate with our allies and partners, or those that we'll carry out through multilateral institutions."

Obama's statement, which came amid reports that Gaddafi's control over the country had receded to little more than the capital, Tripoli, was his first since the weekend when Libyan security forces and, according to a number of reports, foreign mercenaries unleashed a wave of violence, including strafing by Libyan warplanes and helicopters, against anti-government demonstrators in Benghazi and other cities.

Franco Frattini, the foreign minister of Italy, the European country with perhaps the closest ties to its former colony, said Wednesday that reports that "some 1,000" people have died as a result of the repression were "credible", while the Paris-based International Federation for Human Rights estimated that least 700 people had died since late last week.

And while Gaddafi's son and heir apparent, Saif al-Islam Gaddafi, insisted in a televised broadcast late Wednesday that the situation had returned to "normal", Tripoli residents told foreign media by telephone that the capital's population was staying in their homes for fear of being attacked in the streets by security forces and pro-Gaddafi militias.

Meanwhile, foreign reporters in Benghazi, Libya's second largest city, reported that residents there had established a provisional governing authority, while Misurata, the third largest city located just east of Tripoli, fell to anti- Gaddafi forces Wednesday. The government has also abandoned positions along the country's western border with Tunisia, and hundreds of people have fled across the frontier, according to eyewitness accounts.

Despite a number of statements by lesser officials condemning the violence, Obama has faced a rising tide of criticism – mainly from neo-conservatives and other hawks, but also from human rights activists – this week over what they have called his "silence" on the situation and his failure to date to impose sanctions against the regime.

His remarks late in the afternoon appeared intended in part to answer that criticism.

By way of introduction, he stressed that his "highest priority" was to do "everything we can to protect American citizens", of whom there are believed to be about 6,000 residing in Libya.

U.S. officials told reporters on background this week that one reason Obama has been reluctant to personally denounce Gaddafi during the crisis was fear that U.S. nationals could be taken hostage by the regime. Analysts noted Wednesday that Obama did not mention Gaddafi by name in his remarks. At the same time, Obama's statement was the harshest by Washington to date. "The suffering and bloodshed is outrageous and it is unacceptable," Obama said.

"So are threats and orders to shoot peaceful protesters and further punish the people of Libya. These actions violate international norms and every standard of common decency. This violence must stop," he declared.

Obama also suggested for the first time that Washington is actively considering imposing sanctions against the regime. "Like all governments, the Libyan government has a responsibility to refrain from violence, to allow humanitarian assistance to reach those in need, and to respect the rights of its people," he said.

"It must be held accountable for its failure to meet those responsibilities, and face the cost of continued violations of human rights," he added.

On Tuesday, John Kerry, the Democratic chairman of the Senate Foreign Relations Committee who often acts as a stalking horse for the administration, called for the imposition of targeted sanctions against the regime.

Both German Chancellor Angela Merkel and French President Nicolas Sarkozy have also urged the European Union (EU) to immediately take similar action.

Obama made clear that he preferred to coordinate U.S. action with other countries and specifically praised the U.N. Security Council statement issued Tuesday that condemned the violence and called for accountability for its perpetrators.

"This same message, by the way, has been delivered by the European Union, the Arab League, the African Union, the Organisation of the Islamic Conference, and many individual nations," he emphasised. "North and south, east and west, voices are being raised together to oppose suppression and support the rights of the Libyan people."

He also implicitly rejected charges by Gaddafi and other autocratic regimes in the region that the United States was behind the uprising.

"The change that is taking place across the region is being driven by the people of the region," he said in a reference as well to the ouster over the last six weeks of the presidents of Tunisia and Egypt and the continued popular unrest in Bahrain and Yemen.

"This change doesn't represent the work of the United States or any foreign power," he insisted. "It represents the aspirations of people who are seeking a better life."

He announced that he is sending Undersecretary of State for Political Affairs William Burns, who has been in Cairo this week, to Europe and elsewhere in the middle East to "intensify our consultations" about possible measures regarding Libya. He also announced that Clinton herself will travel to Geneva Monday for a foreign ministers' meeting of the U.N.'s Human Rights Council, of which Libya is a member.

A number of critics here have called on the administration to include among any sanctions it takes against Libya the country's expulsion from the Council.

They have also called for Washington and NATO to impose a "no-fly" zone over parts of Libya to prevent the regime's aircraft from attacking anti-government forces. Some critics, mainly from the right, have urged the administration to provide arms to the rebels, as well.

Whether Obama's latest remarks will quiet the criticism remains to be seen.