Majed al-Muhammed, a former medic in the Syrian army who now leads a group of opposition fighters, told The New York Times he has always opposed Muslim extremists. But he said he is angry about the lack of Western military support.
Ghassan Abdul Wahib, 43, a truck driver turned rebel leader in northern Syria, said he is frustrated.
"The United Nations and international community are making a big mistake," he said. "By letting this be a long war, they are dragging Syria toward radicalism, and they will suffer from this for a long time."
There have also been warnings that the fighting in Syria, which reached across the border this week when a mortar round killed five civilians, is shifting public opinion in Turkey.
"We are now at a very critical juncture," Melih Asik, a columnist, said in the newspaper Milliyet. "We are not only facing Syria, but Iran, Iraq, Russia and China behind it as well. Behind us, we have nothing but the provocative stance and empty promises of the U.S."
The Times said Syrian rebels compare the air support given their Libyan counterparts last year to the humanitarian aid they receive. Many believe the United States and European Union countries are relieved to be able to use opposition from China and Russia to avoid sanctions that might cut the oil supply.