The United Nations’ humanitarian chief, Valerie Amos, is in Damascus and on her way to the besieged city of Homs. Amos says her goal is to “urge all sides to allow unhindered access for humanitarian relief workers so they can evacuate the wounded and deliver essential supplies,” but Assad has blocked Red Cross aid convoys from entering the besieged city, citing security concerns. The U.N. says more than 1,500 people from Homs have crossed the border into Lebanon to escape the violence. But that route may become more dangerous: the Syrian opposition says government forces targeted a bridge used by refugees fleeing to Lebanon. Yesterday President Obama called the situation “heartbreaking” but ruled out unilateral military action.