The United Nations Security Council is calling on the Syrian government to grant UN humanitarian chief Valerie Amos "immediate and unhindered access" to the country.
In a unanimously agreed statement, the council's 15 member countries also said that they "deplore" the rapidly deteriorating humanitarian situation in the country.
Amos, who heads the UN Office for the Coordination of Humanitarian Affairs (UNOCHA), said on February 29 that she had been refused permission by the Syrian authorities to enter the country.
In Washington, the assistant secretary of state for Near Eastern affairs, Jeffrey Feltman, said "the demise of the [President Bashar al-] Assad regime is inevitable."
Speaking during testimony before the Senate Foreign Affairs Committee, Feltman added: "It's important that the tipping point for the regime be reached quickly, because the longer the regime assaults the Syrian people, the greater the chances of all-out war and a failed state."
Testifying alongside Feltman, U.S. Ambassador to Syria Robert Ford said: "the Assad regime is under greater stress now, I think, than it was even two or three months ago" due to sanctions and military desertions.
The move comes as Syrian rebels fighting government troops in the city of Homs say they have withdrawn from the district of Baba Amr.
The Free Syrian Army said that most of its fighters had made a "tactical" retreat to spare the lives of the remaining several thousand civilians.
Government forces said they had full control of the district.
Meanwhile, the International Red Cross and Syrian Red Crescent said they had permission to enter Baba Amr on March 2. They plan to bring food and medical supplies, and will also evacuate those in need.
The district has been subjected to nearly a month of bombardment in which activists say hundreds of civilians were killed.
The Syrian Observatory for Human Rights said at least 17 people were killed in fighting on the outskirts of the district on March 1, and that troops were searching for rebels and making arrests.
WATCH: Syrian rebels withdraw from Homs
The yearlong revolt against President Bashar al-Assad's regime began with peaceful protests, but as the crackdown by security forces intensified it was increasingly joined by defectors from the military and people who took up arms.
Earlier on March 1, the main opposition group, the Syrian National Council, said it was setting up a "military bureau" to organize and unify the armed resistance.
British Foreign Secretary William Hague said Britain was closing its embassy and withdrawing all remaining diplomatic staff amid what is described as a worsening security situation.
Earlier on March 1, the United Nations Human Rights Council condemned the Syrian government for what it described as "widespread and systemic violations" against civilians.
Three members of the council -- Syrian ally Russia, as well as China and Cuba -- voted against the resolution at the Council session in Geneva, Switzerland.
The resolution calls on Assad's regime to immediately stop attacks on civilians and grant unhindered access to aid groups.
Thirty-seven of the council's 47 members voted in favor of the resolution, which was sponsored by Gulf Arab nations.
In addition to the "no" votes from Russia, China, and Cuba, three nations abstained and four did not take part.
The resolution is not legally binding.
The United Nations says more than 7,500 people have been killed since the crackdown on protests began.
With AP, Reuters, AFP, and dpa reporting