France and Britain are lobbying the European Union to lift an arms embargo on Syria to raise the possibility of sending weapons to rebel fighters as early as May. So far, the U.S. has joined Germany and other EU nations in resisting supplying arms to opposition forces. But Kerry said this week that the U.S. would not stand in the way of other nations that decide to arm the rebels.
Congress increasingly is pushing the White House to send military aid to anti-regime fighters. On Thursday, Senate Armed Services Chairman Carl Levin, D-Mich., and the panel's top Republican, Sen. John McCain of Arizona, asked Obama to deploy Patriot missiles near the Syrian border in southern Turkey to deter Assad's air forces and destroy regime aircraft. The senators stopped short of asking for arms for rebels, but they encouraged stronger aid to vetted groups, including intelligence, communications equipment and humanitarian assistance, like food and medical care.
"Over the past two years that the horrific conflict in Syria has pressed on, both Syrians on the ground and key allies across the region have made clear their hope for stronger American support," wrote Levin and McCain. "We urge you to take steps to ease the suffering of the Syrian people and protect U.S. national security interests."
Disarray within the opposition forces also has stymied the move to unseat Assad, although rebels control territory in Syria's north and east. Ford described the opposition as divided into political and military wings, and "both are not entirely unified."
This week, the Syrian National Coalition elected American-educated Ghassan Hitto as its prime minister but almost immediately witnessed a walkout by about a dozen of its members, who protested they were sidelined from the decision. The coalition is recognized by the U.S. as a legitimate representative of the Syrian people, but some of its members complain it is dominated by fundamentalists from the Muslim Brotherhood, a conservative Islamist movement.
Additionally, the rebels have been joined by what Ford described as a small minority of fighters known as Jabhat al-Nusra, a powerful offshoot of al-Qaida in Iraq. Al-Nusra has claimed responsibility for most of the deadliest suicide bombings against regime and military facilities and, as a result, has gained popularity among some rebels. However, the group has alienated secular-minded fighters, which is one reason the U.S. has not equipped the rebels with weapons. The Obama administration designated al-Nusra as a terrorist organization last December.
Western nations worry that al-Nusra or other rebels will get their hands on Syria's chemical weapons stockpile — but are as concerned that Assad will use them against his people, although he has vowed not to. Ford declined to discuss how the White House would retaliate if Assad crosses Obama's red line and deploys the deadly chemicals, but he said the regime might be more tempted to do so as it loses ground.
Ban said he was aware of charges that Assad's military used chemical weapons against the rebels in the Aleppo attack. But the secretary-general did not make clear whether the rebels' claim also would be part of the new U.N. probe. Obama, meanwhile, has said he is "deeply skeptical" that opposition forces used the chemical weapons.
Because of the risks getting investigators to the war zone, it likely will be difficult to prove whether chemical weapons were used, said Ralf Trapp, a chemical and biological weapons scientist formerly at the Organization for the Prohibition of Chemical Weapons. He said evidence is best collected at least within several miles from the site at the time of the attack.
"You really have to be on the ground," Trapp said in a telephone interview from France. "You need to be where the event occurred and you need to speak with the victims. In a civil war, that's not easy."
Ford said the rebels have begun to outmatch the regime's military and captured key cities and officials while controlling Syria's land borders with Turkey and Iraq. Heavy fighting near Assad's palaces in Damascus recently "would have been rattling his windows," Ford said.