Obama calls bloodshed in Syria "heartbreaking" but warns that getting "more entangled militarily in Syria is a serious step."

Referring to the presence of al-Qaeda adherents or other dangerous elements within the Syria armed opposition, Obama said it's important to "know who we're helping."

Romney repeated his pledge to arm the Syrian opposition but didn't say whether he would go any farther. Getting the right weaponry to the rebels can help them topple Syrian President Bashar al-Assad, Romney said.

Obama referred to the assassination of an anti-Syrian official in Lebanon but neither candidate has yet addressed whether the Syrian conflict is spilling over to its smaller neighbor.