"He is also someone who can influence and help rein in extremist groups who have hijacked our revolution," al-Rami said.
Foreign fighters and Islamic extremists, including the al-Qaida inspired Jabhat al-Nusra group, are gaining influence in Syria, which has discouraged the West from giving military aid to rebels, fearing the weapons will end up in the wrong hands.
But some opposition figures believe Washington could give its tacit support to others funneling weapons if the new broad-based rebel coalition holds together and gains international legitimacy, winning recognition from the Arab League and other groups.
In an interview with broadcaster Al-Jazeera aired Tuesday, al-Khatib said the international community has a "moral and legal" obligation to side with the united opposition leadership.
He declined to say whether Qatar or Gulf allies would begin shipping heavy weapons to the rebels, but made clear that efforts to increase the rebel arsenal is a top priority. He suggested that rebel forces could impose their own no-fly zone if given heavy weapons.
"Give them the means to defend themselves, and they will create their own no-fly zone," he said in fluent English.
Al-Khatib also said he supports a tolerant, Islamic state that respects everyone including secular Syrians.
"Any garden is so nice if full of flowers of all kinds," he added.