(CBS) -- The battle between the two branches of Islam is raging in Syria. Secretary of State John Kerry urged Syrian rebels to join peace talks next week in Switzerland. But that won't be easy, because various rebel groups fighting to overthrow the Syrian government are also fighting each other.
On Turkey's border with Syria, hundreds of trucks are backed up for miles. Heavy clashes between rival Syrian rebel groups mean much-needed food aid and medical supplies aren't getting to the people who need them.
Mariam Hoja fled across the border Thursday with her husband and two children. She told CBS News they came from their village near Aleppo where the fighting left them under a state of siege for a week.
“We couldn't even buy food for the children,” she said.
After nearly three years of civil war, the Syrian opposition to President Assad has fractured. Extremist groups with links to al Qaeda are now fighting against other rebels, reportedly leaving hundreds dead.
Just over the Turkish border is a safe house for rebel fighters. None would show their face for fear of retribution against family members inside Syria. They're part of the so-called moderate opposition, backed by the U.S.
But their commander told us that even now -- when they're fighting both the regime and extremist groups -- America isn't helping them.
Asked if they’re getting any arms, any guns at all from the U.S., the commander replied, “No. No…nothing.”
He told CBS News they're relying on homemade weapons, and have seen thousands of their men defect to better-equipped groups, including those linked to al Qaeda.
As the civil war grows deadlier -- and more complicated -- he said he blames America for allowing Islamic militant groups to get the upper hand.
“The children in Syria (they're) killing, the woman in Syria (they're) killing,” he said. “No problem. For the U.S., no problem.”
With less than a week until peace talks are due to begin in Geneva, the Syrian opposition is in disarray, and this infighting is strengthening the position of the Syrian regime.