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And I'm Robert Siegel.
We begin this hour in Syria, where Islamist militants and groups with links to al-Qaida are playing a larger role in battles against Syrian troops. But there's also serious tension between these radicals who've joined the revolution and Syria's homegrown rebel fighters. The latest evidence of that tension, NPR's Deborah Amos reports, is the kidnapping and reported murder of the leaders of a militant brigade in northern Syria.
DEBORAH AMOS, BYLINE: This border crossing, Bab Hawa, on Syria's northern frontier, was the site of a training camp for a militant Islamist group until a few weeks ago. They are gone, and it's for the good of Syria, said one rebel with knowledge of the operation to eliminate a group linked to al-Qaida.
Now, at this checkpoint, the black banner of the brigade of the Islamic state has been replaced with the flag of Syria's revolution. Syrians crossing the border confirmed that just a few of the foreign fighters remain.
ABU MAHMOUD: They are still there. We talked to them a little bit. The head of them, he was killed. He was assassinated.
AMOS: Syrian activist Abu Mahmoud(ph) says the leader of the brigade, Muhammad al-Abseh(ph), was a Syrian, but his fighters were radicals from abroad. A rebel source says al-Abseh trained in an al-Qaida camp in Afghanistan in the 1980s.
UNIDENTIFIED MAN #1: Once he's killed, then this unit of al-Qaida - this was strong unit - they were dispersed and paralyzed.
AMOS: This was the first direct confrontation between Syrian rebels and Islamist radicals. The Farouk brigade provoked the fight, the largest of the homegrown rebel groups. The dispute started over a flag, the black banner of the brigade of the Islamic state, says Adib Shishakli(ph), a Syrian opposition politician.
ADIB SHISHAKLI: This is a flag of an Islamic state or al-Qaida.
AMOS: But the flag raised larger concerns, he says, that radicals are trying to hijack the revolt.
SHISHAKLI: This is not a political playground for everybody to come with his own agenda and try to execute it.
AMOS: The death of an extremist is a sign of the internal dynamics of the fight to topple the regime and the intense competition for guns and money to continue the fight. A new study by the London-based Quilliam Foundation that tracks radical groups reports extremists make up less than 10 percent of Syria's rebels, but warns their influence is growing because they're better funded and armed.
In a crowded apartment on the Turkish border, these Syrian officers, recent defectors, say more extremists are joining the revolt. They complain bitterly that money is pouring in from private donors who support radical ideologies. Abu Mohammed(ph), a military doctor, blames the West for failing to back Syria's moderate rebel groups.
ABU MOHAMMED: (Through translator) When I am desperate and I need weapons, guns, and I find those guys full with those things, I will join them.
AMOS: Do you think it gives the revolution a bad name?
MOHAMMED: (Through translator) The Western world create al-Qaida in Syria because of doing nothing.
AMOS: Western governments are debating how much support to give the rebels. Concern over extremists has stalled a definitive answer.
UNIDENTIFIED MAN #2: We lost our guy.
AMOS: Here at the border, rebels say that al-Abseh, the extremist leader, had to go. Mahmoud Najar(ph), a rebel fighter, who says he learned his English from watching American movies, says it sends a good message now that al-Abseh is dead.
MAHMOUD NAJAR: Because he give a wrong picture about us. The real Islam is not like they understand it.
AMOS: We're not extremists here, says Najar. And those radicals, they're against us too.
NAJAR: They do so wrong things to us. So they must be captured, all of them.
AMOS: The rebels here at Bab Hawa eliminated one extremist group. But as this conflict grinds on, more are joining the fight. Deborah Amos, NPR News, Antakya.