The United States hinted at an international coalition on Syria following a United Nations attempt to end nearly 11 months of bloodshed was vetoed over the weekend, the Associated Press reported.
The move comes after Russia and China vetoed a UN Security Council resolution on ending the violence in Syria and amid fears that the conflict could turn into a civil war.
"What happened yesterday at the United Nations was a travesty," Clinton said during a visit to Bulgaria following a meeting in Munich with Russian Foreign Minister Sergei Lavrov, Agence France Presse reported.
"We will work to expose those who are still funding the regime and sending it weapons that are used against defenseless Syrians, including women and children," Clinton said. "We will work with the friends of a democratic Syria around the world to support the opposition's peaceful political plans for change."
More from GlobalPost: Protests spread to Syrian embassies worldwide
On the ground, the commander of the Free Syrian Army told the AP that now "there is no other road" except military action to topple Assad.
British Foreign Secretary William Hague said China and Russia will be "held responsible" for the violence in Syria and that they made a "great mistake," the BBC reported.
Russian Foreign Minister Sergei Lavrov is due to go to Syria on Tuesday with Foreign Intelligence Service Director Mikhail Fradkov for talks with Assad, Reuters reported.
Britain-based Syrian Observatory for Human Rights said at least 30 civilians were killed Sunday, including five children and a woman who was hit by a bullet while standing on her balcony as troops fired on protesters in a Damascus suburb.
Human Rights Watch warned the Syrian government "against interpreting the double veto as a green light for even more violence."