ALEPPO, Syria and BEIRUT, Lebanon — As evidence mounts that foreign Islamists are fighting alongside Syria’s increasingly radicalized rebels, Christians in Aleppo and elsewhere are taking up arms, often supplied by the regime.

“We saw what happened to the Christians in Iraq,” Abu George, a Christian resident of Aleppo’s Aziza district told GlobalPost. “What is going on in Aleppo is not a popular revolution for democracy and freedom. The fighters of the so-called Free Syrian Army are radical Sunnis who want to establish an Islamic state.”

While the 30-year-old shopkeeper said he had not received any direct threats from Syria’s Sunni Muslim rebels, he fears a repeat of Iraq’s sectarian bloodletting.

Since the 2003 US-led invasion of Iraq, the UN Human Rights Council estimates around half of Iraq’s 1.4 million Christians have fled the country, driven out by nearly a decade of church bombings, kidnappings and sectarian murder.

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The plight of Christians in Iraq has long worried Syria’s estimated two million Christians, around 10 percent of the population. The nightmare of similar persecution has led them to support the secular regime of President Bashar al-Assad, which presents itself as a defender of minorities.

With Syria now gripped by civil war and the Assad regime fighting for its survival, however, Christians like Abu George fear retribution, already occuring in some parts of the country, from the Sunni-led rebels they refused to back.

In Qseir, a town of some 60,000 people southwest of Homs, which has been under siege by regime forces for at least seven months, mosques recently rang out with the call for all Christians, who numbered around 10,000, to leave.

The breakdown of inter-communal relations in Qseir stems from both rising fundamentalism among Sunni fighters and the widespread belief that Christians had been collaborating with the Assad regime.

Just 10 miles from the border with Lebanon, Qseir Sunni fighters are increasingly radicalized. Some openly identify themselves as mujahadeen fighting for an Islamic Caliphate rather than simply the overthrow of the Assad dictatorship.

“We fight to raise the word of God,” said Abu Salem, a 29-year-old Syrian from Qseir, recuperating recently in the no-man’s-land border between Lebanon’s northern Bekaa Valley and Syria.

As shells exploded less than a mile away, the former cement mixer showed photos on his mobile phone of Osama Bin Laden and the latest videos from Al Nusra Front, the little known jihadi group that has claimed responsibility for many of the biggest bombings to hit Damascus since January.

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“After the regime is toppled this will be the first stone in building the Islamic Caliphate and Syria must adopt Islamic law,” he said.

The skinny fighter said his group, the Mujahedeen Brigade, was led by a Syrian who fought against US troops in Iraq’s Fallujah. Abu Salem said he received money from Syrian expatriates in the Gulf and that it came with the greeting that is commonly used by ultra-conservative Salafists.

While Abu Salem’s claims were impossible to verify, there is little doubt that Qseir’s Sunni fighters have grown increasingly radicalized over the past six months.

More from GlobalPost: Syria: The new land of jihad?

Abu Ali, a military intelligence officer who defected to the rebels and was first profiled by GlobalPost last November, and then again in a video published in March, now leads Qseir’s Wadi Brigade, one of the town’s largest and strongest rebel groups.

Interviewed regularly over Skype over the last six months, Abu Ali has expressed increasingly fundamentalist and intolerant views. He once called for foreign military assistance. But now he says that if international forces join the fight against Assad, “they would be the ones we target, even before the regime.”

Injured by shrapnel at least twice since joining the fight in Qseir last December, Abu Ali has grown a thick beard. Increasingly conservative, he criticized a Muslim reporter for smoking during a Skype call, citing the current period as a time of “holy war.”

Abu Ali said he supported the call for Christians to leave Qseir, accusing them of collaborating with the regime.

In interviews with more than a dozen Qseir residents, a Wall Street Journal reporter recently discovered a vicious cycle of murder and kidnap between Sunni and Christian families, triggered by claims that Christians were acting as regime spies. Almost all Qseir’s Christians have now fled, with many taking shelter in makeshift tents in the northern Bekaa valley.

“I used to work as a legal consultant, but now I live like a beggar here in Lebanon,” said a woman who gave her name as Marta and who said her husband had been kidnapped. She said her home in Qseir had been taken over by rebels and destroyed.

Abu George, from Aleppo, said officials from the ruling Baath Party had offered prominent Christians in Aziza and other Christian-majority areas of Aleppo “AKs and pistols” late last year. The weapons, they were told, were to protect themselves against the “armed gangs” the regime claimed to be fighting.

For the first year of Syria’s uprising, Aleppo remained largely untouched by the mass protests seen in opposition strongholds like Homs and Hama.

More from GlobalPost: Aleppo, Syria’s sleeping giant, stirs

Today, however, Abu George sees the regime’s control over Aleppo as slipping, directly threatening his community.

“The armed fighters took over the Midan police station, very close to the Christian quarters. There are no police there now, so how can we live? We see on TV armed young men with beards shouting, ‘God is great!’ and calling for jihad. We have the right to defend ourselves.”

The exact number of Christians in Aleppo, a city of three million people, is not known but estimates vary between 100,000 and 250,000.

Like Abu George, Abu Omar al-Halaby was a shopkeeper who has taken up arms. But Abu Omar is a Sunni, a fighter with the Brigade of Unification, one of the largest rebel groups holed up in Aleppo’s Salah Adeen quarter.

Speaking to GlobalPost, Abu Omar said his unit had deliberately not deployed in Christian areas in order not to inflame communal tensions. “We are very concerned for civilians and have been working to get people out and to safety,” he said.

Abu Omar said he wanted the right “to go to a mosque, have a long beard and practice my Islamic duties freely” and said much of his motivation to fight stemmed from the religious persecution he saw his father suffer under Hafez al-Assad, Syria’s former dictator.

“My father was arrested for 15 years just because someone who hated him wrote a report to the security services, accusing him of being a member of the (banned) Muslim Brotherhood,” he said.

“He was not, but he was a religious man who spent time at the mosque. A piece of paper took him away from us. Three months after he was released from prison, he died.”

GlobalPost's James Foley, who is inside Aleppo, talks to the PBS Newshour:

Watch Refugees, Rebels Flee Syria Conflict Areas as Troops Advance on PBS. See more from PBS NewsHour.

As religious and sectarian hatred intensify, Syrian rebels are being joined by foreign jihadis, some of whom have reportedly fought in Iraq, Afghanistan and even Yemen.

Last week, a Dutch and a British photographer in northern Syria were released from captivity at what they said was a training camp for between 30 and 100 foreign jihadis, who repeatedly threatened to kill them.

“They were only foreign jihadis; I don’t think there was one Syrian among them,” Dutch photographer Jeroen Oerlemans told the New York Times. “All day we were spoken to about the Quran and how they would bring sharia law to Syria. I don’t think they were Al Qaeda, they seemed too amateurish for that. They said, ‘We’re not Al Qaeda, but Al Qaeda is down the road.’”

Standing guard at the Salama border crossing near Turkey, a rebel known as Abu Sadiq told GlobalPost last week that since they had seized that and other crossings on Turkish and Iraqi borders, “more Arab fighters had entered the country to fight with us against the Assad regime.”

Abu Sadiq said the foreign fighters included men from Saudi Arabia, Yemen, Algeria and Libya and that many he had met said they were inspired to come to Syria after seeing the news on the massacres in Houla and Homs.

“We try to keep the non-Syrian fighters out of sight as we don’t want them hurting us with their radical ideas. The Assad regime brings Shiites from Iran, Iraq and Lebanon and Russian military experts so we have the right to ask for help from Sunni nations,” Abu Sadiq said.

“The regime made this a sectarian war against the Sunnis. Syria is not Afghanistan, but right now we need help from anyone.”

A GlobalPost reporter contributed from Aleppo, Syria, Hugh Macleod and Annasofie Flamand contributed from Beirut, with additional reporting by Rami Aysha.