The White House accused Syria's Bashar al-Assad on Wednesday of unleashing helicopters, airplanes, and tanks on civilians in the city of Aleppo, calling the assault evidence of his willingness to sink to "the depths of depravity."
Press secretary Jay Carney, speaking aboard Air Force One, confirmed that Syria's ambassadors to the United Arab Emirates and Cyprus had defected from the regime.
"This is another indication, we believe, that senior officials around the Assad inner circle are fleeing the government because of the heinous actions taken by Assad against his own people, and the recognition that Assad's days are numbered," Carney said.
The spokesman highlighted Assad forces' onslaught on Aleppo and cited "credible" but unconfirmed reports that the regime in Damascus had deployed airplanes in the attack.
"We condemn that. And it's just another indication of the depths of depravity that Assad has demonstrated himself capable of achieving," Carney said.
Asked about speculation that Russia, which blocked action on Syria at the U.N. Security Council, might be softening its support for Assad, Carney would only say Washington and Moscow are in regular talks about the bloody conflict.
"As we've seen in Aleppo today, the longer we go, the more willing Assad is to take extreme measures to kill his own people," he warned.
"We and our partners have been and will continue to take steps to isolate the Assad regime, to starve it of financial resources through sanctions, which makes it increasingly difficult for Assad to finance his brutal crackdown on his own people," Carney said.
The Obama administration has faced criticism from Mitt Romney and other Republicans, including Senator John McCain, that it has not taken a hard enough line on Assad. McCain has called for arming the rebels. Others have suggested the creation of safe havens defended from Syrian troops. Obama has refused to take a direct role in arming the opposition to Assad, but officials say Washington has been providing humanitarian and logistical aid. And there are news reports of an American role in vetting rebels for arms shipments from other countries.