The pledge would bring the U.S. contribution to the Free Syrian Army to $25 million, the U.S. State Department said in a release.
"U.S. assistance includes medical supplies and other humanitarian relief for displaced and vulnerable and besieged Syrian communities. As part of a growing international effort to quickly and effectively deliver aid into Syria as access and conditions allow, we are also bolstering existing regional food and relief supply stockpiles and the logistical capacity needed to deliver these humanitarian supplies," the statement read.
Clinton said Syrian President Bashar Assad was "adding to its long list of broken promises," by failing to accept and implement a plan by United Nations Arab League envoy Kofi Annan that will end the violence.
The 60 Arab and Western leaders, known as the Friends of Syria group, are meeting in Turkey to discuss coordinating sanctions against Syria "to isolate this regime, cut off its funds and squeeze its ability to wage war on its own people," Clinton said.
"Stop killing your fellow citizens or you will face serious consequences," she added.
Meanwhile, at least nine people were killed in Syria's Daraa region Sunday.
Unnamed opposition activists told CNN gunfire and explosions were heard in Damascus where the Syrian Army deployed tanks at various checkpoints and snipers on rooftops targeted moving objects.