Kerry acknowledged the need to change the military "imbalance" on the ground in order to change al-Assad's "calculus."
"Right now, President Assad is receiving help from the Iranians, he's receiving help from al Qaeda-related, some elements, he's receiving help from Hezbollah, and obviously some help is coming in through the Russians," Kerry said. "If he believes he can shoot it out, Syrians and the region have a problem and the world has a problem."
Members of the rebel Free Syrian Army have said they've received shipments from some countries and seized and purchased weapons from government troops. But al-Assad's forces have heavy weaponry and warplanes.
Last week, the French foreign minister said he wanted to lift a European Union arms embargo and start arming rebels.
"We must go ahead and allow the Syrian people to defend themselves against this bloodthirsty regime. It's our responsibility to help the (opposition) Syrian National Coalition, its leaders and the Free Syrian Army by all the possible means," Laurent Fabius wrote in an op-ed for the French newspaper Liberation.
"If not, the slaughter will continue, and there will not be any other possible outcome but to strengthen the most extreme groups and the collapse of Syria with devastating consequences for the country itself and the region."
In February, the European Union renewed its arms embargo on Syria for three months -- but amended it to allow greater nonlethal support and technical assistance to help protect civilians.
The latest EU arms embargo is set to expire in May. Member countries could renew it, add amendments or veto it.
A new opposition leader
A Syrian opposition alliance elected Ghassan Hitto, an information technology executive and U.S.-educated Kurdish businessman, to lead its provisional government.
The National Coalition for Syrian Revolutionary and Opposition Forces made the announcement Tuesday.
The contingent government's formation should assuage concerns from the West -- particularly the United States -- about who would lead Syria should al-Assad be deposed, the Syrian American Council said.
"This question has now been answered," the group said.
For two years, the lack of a clear alternative to al-Assad's government has hampered the opposition's efforts in gaining more international support. Some say the absence of an alternative leader has helped prolong the bloodshed.
It didn't take long for Hitto to declare what many in the opposition have said: "There will be no dialogue with the Assad regime."