The gunmen in eastern Syria, wielding grenade launchers and assault rifles, announced on the Internet they were forming the "God is Great" Brigade and joining the country's rebellion. They swore allegiance to the Free Syrian Army and vowed to topple President Bashar Assad.
But unlike many other rebel bands, they wrapped their proclamation in hard-line Islamic language, declaring their fight to be a "jihad," or holy war, and urging others to do the same.
"To our fellow revolutionaries, don't be afraid to declare jihad in the path of God. Seek victory from the One God. God is the greatest champion," the brigade's spokesman said in the January video. "Instead of fighting for a faction, fight for your nation, and instead of fighting for your nation, fight for God."
As Syria's uprising evolves into an armed insurgency, parts of the movement are taking on overt religious overtones. Islamic movements in and out of the country are vying to gain influence over the revolt in hopes of gathering power if Assad falls.
The Islamists' role complicates choices for the United States and other nations who say they want to help the opposition without empowering radicals; a string of anti-regime suicide bombings have raised fears of al-Qaida involvement.
The groups diverge from violent jihadi movements to political moderates like the Muslim Brotherhood, which has already used the Arab Spring revolutions to vault to power in Tunisia and Egypt elections.
Their growing influence is seeding divisions within an already fractured opposition. A week ago, several prominent figures quit the Syrian National Council, the body of exiles that has tried to emerge as the opposition's political leadership. They complained the fundamentalist Brotherhood dominates the group.
The council is "a liberal front for the Muslim Brotherhood," said Kamal Labwani, a veteran secular dissident, who broke away. He said the Brotherhood was trying to build allegiances on the ground in Syria.
"One day we will wake up to find an armed militia ... controlling the country through their weapons," Labwani said.
The U.S. has rejected sending arms to rebels, fearing a sectarian civil war. U.S. officials also warn that al-Qaida's militants in Iraq are infiltrating Syria _ worries heightened by attacks in Damascus and Aleppo using al-Qaida's signature tactic, suicide bombings.
An Islamic militant group, the Al-Nusra Front, on Tuesday claimed responsibility for a double suicide bombing that killed 27 people in Damascus over the weekend. The group appears to be a front for al-Qaida's Iraq branch, said a U.S. official, speaking on condition of anonymity to discuss matters of intelligence.
Judging the extent of Islamist influence in Syria's uprising is difficult, in part because Syria has largely prevented journalists from reporting on the conflict.
Opposition activists are reluctant to talk about any Islamist role because Assad's regime depicts their movement as solely a campaign by terrorists and Islamic radicals. Such rhetoric is highly effective in scaring religious minorities and moderate Sunnis away from supporting the uprising.
But activists acknowledge Islamists could have appeal for an opposition bloodied by Assad's brutal campaign against the uprising, which the U.N. says has left more than 8,000 dead.
"Repression breeds extremism," said Omar, a student activist in Damascus. "People left on their own will resort to anything and anyone to help them." He gave only his first name for fear of reprisals.
Syria's uprising is profoundly divided. The revolt has been led by the country's Sunni Muslim majority and reflects the community's diversity, from the secular to the religious, united by the drive to oust Assad.
_ There are the masses of peaceful protesters around the country, organized largely by local youth activists. These tend to reflect the makeup of towns or cities where they take place _ some areas are more conservative than others. Since protests began, organizers have sought to keep them non-ideological. Protests are often festive in tone, with dancing and songs. But slogans for "jihad" have popped up in some places.
_ There are the armed rebels _ soldiers who defected from Assad's army and locals who have taken up weapons. Usually, a unit of defecting soldiers or other fighters in a particular area announces the formation of a "brigade," often in an Internet video like that of the "God is Great" Brigade, a group of fighters in the eastern region of Deir el-Zour.
Most declare nominal allegiance to the Turkey-based Free Syrian Army. But the brigades appear to be largely on their own in finding weapons and organizing.
Some brigade videos feature no Islamic rhetoric, while others are rich with the rhetoric of ultraconservative movements _ suggesting they back hard-line agendas.
The Free Syrian Army's leadership in Turkey is secular-leaning, and there have been reports of frictions with the Brotherhood that have made the army reluctant to work closely with the council.
Ultraconservative Islamists known as Salafis are gaining ground among some factions. Salafis preach a strict doctrine similar to that in Saudi Arabia and contend that no law but Islamic Shariah law is permissible.
Sheikh Adnan al-Arour, a Syrian Salafi cleric based in the Gulf, regularly appears in fiery monologues on Saudi TV channels calling for jihad against the "infidel" Assad regime.
His influence is shown by the open allegiance declared by several rebel brigades. One, called the "Supporters of God Brigade" in Hama, praised him as "the leader of the revolution" in February.
_ Finally, there is the Syrian National Council, the 270-member group made up mainly of exiles headed by secular dissident Burhan Ghalioun. It has tried with little success to gather the opposition under its umbrella.
A video posted on YouTube last week showed a former Syrian Brotherhood leader, Ali Sadr el-Din Bayanouni, admitting the Brotherhood nominated Ghalioun as council leader merely as a "front" more easily accepted by the West.
"We did not want the Syrian regime to take advantage of the fact that Islamists are leading the SNC," Bayanouni says in the video.
A London-based Brotherhood spokesman, Zuhair Salem, denied the group was trying to dominate.
"We joined the revolution to bolster it, not to control it," he said.
The Brotherhood has had no organization on the ground since the 1980s, when it waged a violent campaign, assassinating regime figures. Assad's father Hafez Assad retaliated by almost destroying their main stronghold, the city of Hama, killing thousands and sending members fleeing abroad. Since then, mere Brotherhood membership has been punishable by death.
Ex-council member Labwani and others in the opposition say the Brotherhood is using the council to rebuild by distributing money and weapons, key levers for influence. The Brotherhood has a powerful donor network among members in exile and supporters in oil-rich Gulf countries.
Khalaf Dahowd, from the opposition group the National Coordination Body, said Brotherhood domination of the council "has led to doubts and suspicions among the more secular factions in Syria about the post-Assad period."
It is unclear how much weaponry is reaching rebels, most of whom complain they receive no outside help. That illustrates the difficulty of any group dominating the opposition amid the divisions and regime onslaught.
But Islamists appear to be maneuvering for their chance, said Bilal Saab, a Middle East expert at the Monterey Institute of International Studies in California.
The Brotherhood "are lying low, waiting to see how events unfold and reap the fruits of the fight."
Keath reported from Cairo. AP correspondent Kimberly Dozier contributed from Washington.