John Ging, director of operations for the Office for the Coordination of Humanitarian Affairs, said members of a survey team were appalled by the devastation in cities like Homs, which has bore the brunt of the 20-month conflict.
He said in a statement that he was "encouraged that the delegation was able to cross the conflict lines, which demonstrates that, where there is political will, there is a way to ensure that international humanitarian law and humanitarian principles are upheld, even during such intense conflict."
The United Nations estimates at least 60,000 people have died as a result of war. Humanitarian workers have been unable to address the needs of the estimated 650,000 people displaced by conflict.
"The humanitarian needs are enormous," added Ging.
Brahimi, a veteran Algerian diplomat, told the BBC this month that a rhetoric of change spelled out by Syrian President Bashar Assad in a New Year's address didn't make "one iota" of difference for peace.