Pressure is mounting for Syrian president Bashar al-Assad to quit his nation as Western and Arab nations indicate they are willing to broker a deal for his exit.
Clinton's comments come after her close friend, Senate Intelligence Committee Chairwoman Dianne Feinstein, a California Democrat, also voiced support for getting Assad out of Syria.
The offer comes despite UN High Commissioner for Human Rights, Navi Pillay, having said earlier this year that there was ample evidence to prosecute Assad for war crimes.
Meanwhile, signs that Assad's regime is teetering on the brink after 16-months of bloodletting in Syria's popular Arab Spring uprising turned civil war continue to emerge.
Lamia al-Hariri is the second Syrian diplomat to join the opposition, following Nawaf Fares, the ambassador to Iraq, who defected earlier in July. Fares was also reported to be in Qatar.
Opposition groups claimed warplanes, seen circling high above, had launched airstrikes in Aleppo on Teusday, as deadly clashes continue to leave scores dead each day.
Opposition activist Mohammed Saeed has estimated the rebels are holding large chunks of the city and the government has responded with attack helicopters.
"Helicopter and tank shells are falling on areas in the outskirts of Aleppo, which came under the control of the rebels," activist Abu Haytham al-Halabi told dpa by phone.
Nevertheless, rebel fighters from the Free Syrian Army have turned Syria's once impregnable leading cities into fiercely contested battlegrounds in recent weeks.
"Aleppo has joined Homs and Hama and other revolutionary cities."
But opposition sources say Washington has yet to turn over tens of millions of dollars in frozen Assad regime dollars promised to rebel factions months ago.
Officials in Washington have been reticent to openly arm and equip Syria's disparate rebel factions out of concern the munitions may fall into the hands of anti-American terror groups.
Earlier this week,Assad's regime has threatened to use chemical weapons should outside forces seek to aid Syria's rebels in toppling his regime.
"Most of us in the Free Syrian Army command know very well where these weapons are located," Colonel Kassim Saadeddine told Al Jazeera.
The London-based Syrian Observatory for Human Rights say at least 19,000 people - most of them civilians - have been killed in Syria since violence erupted March 2012.