"Pouring more arms to the opposition would bring more arms to the government and that will not solve the problem," Brahimi told Channel 4 on Friday.
Syria has been engulfed in a civil war, now in its third year, between forces loyal to President Bashar Assad and those who would like to see him out of power. At least 70,000 people have been killed in the conflict.
Brahimi said the way to end the war is to get both sides to come to an agreement, not for one side to win a military victory, The Guardian MiddleEastLive blog reported.
"What really needs to be done is to work effectively, all of us -- Syrians, the region, and the international community -- for a political solution to the conflict -- that is the only help," Brahimi said.
He said there is a need for more international aid for refugees, describing their situation as "extremely bad."
Mouaz al-Khatib resigned Sunday as president of the National Coalition for Revolutionary and Opposition Forces, although other coalition leaders refused to accept his resignation and it was unclear whether Khatib would return to the coalition.
Fawaz Gerges, director of the London School of Economics Middle East Studies Center, said Khatib's resignation "threatened the very survival of the coalition as a representative of the Syrian people."
"The Syrian opposition is going through a crisis right now," Amr al-Azm, a Middle Eastern scholar at a Shawnee University in Ohio who monitors Syrian politics, told Voice of America.