Updated 5:05 PM ET
(CBS/AP) BEIRUT - The U.N. humanitarian chief got the first look inside the shattered district of Baba Amr on Wednesday but found most people already had fled the rebellious neighborhood in Homs following a devastating military siege.
Activists have accused the government of sealing off Baba Amr for nearly a week while it tried to cover up evidence of atrocities over the past month.
The New York-based U.N. humanitarian chief Valerie Amos arrived in Damascus earlier in the day, then headed straight to the Baba Amr, which the military wrested from rebel control last Thursday after a battle that lasted nearly four weeks. Homs is one of the strongholds of Syria's year-old uprising to oust authoritarian President Bashar Assad.
"The Syrian Arab Red Crescent stayed about 45 minutes inside the neighborhood," ICRC spokesman Hicham Hassan said in Geneva. "Volunteers say that most inhabitants have left Baba Amr to areas that have already been visited last week by the Red Crescent and the ICRC."
Amos is scheduled to meet the head of the Syrian Red Crescent, Abdulrahman Attar, on Thursday,according to CBS News' George Baghdadi. Syrian Foreign Minister Walid Muallim told her that the government would co-operate with her team and was trying to help civilians.
The siege of Baba Arm outraged the international community, and the U.S. said Assad was acting like a war criminal. One powerful U.S. senator, John McCain, is advocating U.S. airstrikes to end Assad's crackdown on the opposition. But Defense Secretary Leon Panetta pushed back against the demands.
"What doesn't make sense is to take unilateral action right now," Panetta told the Senate Armed Services Committee about advising President Barack Obama to dispatch U.S. forces. "I've got to make very sure we know what the mission is ... achieving that mission at what price."
The government has kept Baba Amr sealed off over the past six days, saying it was too dangerous for humanitarian workers to enter. But activists say the government has been engaged in a "mopping-up" operation to hide their activities.
"They haven't let anyone in for a week, and now they are going to let them in?" Homs activists Tarek Badrakhan told The Associated Press. "Today it's simple: They finished their crimes and hid all the proof. Now they think they can show that everything is normal."
Khaled Erq Sousi, head of the emergency committee of the Syrian Red Crescent, confirmed that Amos was on the trip.
Amos has said the aim of her visit is "to urge all sides to allow unhindered access for humanitarian relief workers so they can evacuate the wounded and deliver essential supplies."
The trip comes as Syrian President Bashar Assad defies mounting international pressure to end the year-old crackdown on an uprising against him.
According to state news agency SANA, Assad said Tuesday that he will continue to confront "foreign-backed terrorism." Since the uprising began last March, he has blamed armed gangs and foreign terrorists for the unrest, not protesters seeking change.
Local coordination committees in Syria put Tuesday's death toll at 40. The U.N. says more than 7,500 people have been killed since Syria's uprising began. Activists put the death toll at more than 8,000.
In Washington, Senator McCain, the top Republican on the Senate Armed Services Committee, said the estimated 7,500 dead in the Syrian uprising calls for U.S. leadership that a Democratic president, Bill Clinton, displayed during the Bosnian war in the 1990s and that Obama eventually showed on Libya last year.
"In past situations, America has led. We're not leading, Mr. Secretary," McCain told Panetta.
The Pentagon chief later added that the United States is not holding back and is leading in Iraq, Afghanistan, Syria and the war on terrorism.
Testifying before the committee, Army Gen. Martin Dempsey and Panetta offered a cautionary note to the call by McCain to launch U.S. airstrikes against Assad's regime.
"This terrible situation has no simple answers," Panetta told the panel.
Despite the growing bloodshed, President Barack Obama said Tuesday that unilateral U.S. military action against Assad's regime would be a mistake.
The United States said it is proposing a new United Nations Security Council resolution demanding an end to violence in Syria, first by government forces and then by opposition fighters. Russia and China, powerful Syrian allies that have blocked a Security Council resolution against Syria, have made clear they were still standing by the regime in Damascus.
Mr. Obama has resisted calls to step into the turmoil in Syria to stop Assad's bloody crackdown on protesters. He told a news conference Tuesday that the international community has not been able to muster a campaign against Syria like the one in Libya that ousted Muammar Qaddafi last year.
"For us to take military action unilaterally, as some have suggested, or to think that somehow there is some simple solution, I think is a mistake," Mr. Obama said. "What happened in Libya was we mobilized the international community, had a U.N. Security Council mandate, had the full cooperation of the region, Arab states, and we knew that we could execute very effectively in a relatively short period of time. This is a much more complicated situation."
Mr. Obama's strategy has been to use sanctions and international diplomatic isolation to pressure Assad into handing over power.