The threat of jihadist intervention in Syria's 13-month-old uprising against the minority regime of President Bashar al-Assad is growing, particularly because the opposition forces are so fractured.

"Jihadis will inevitably be part of the picture as the regime cracks down on all opposition and pushes society to the brink, as people feel forsaken by the West and as Persian Gulf states step in to help," said Peter Harling of the International Crisis Group, a conflict resolution think tank in Brussels.

"But the question is how big a role will they carve out for themselves?"

Al-Qaida and its allies had little to do with uprising against Assad's brutal regime, which is dominated by minority Alawites, a Muslim sect affiliated with Shiite Islam and which controls Iran, Syria's main ally.

Syria's population of 22.5 million is 74 percent Sunni, like al-Qaida. The Syrian branch of the Muslim Brotherhood, a Sunni group that's been the godfather of virtually every radical Islamic group since it was founded in Egypt in the 1920s, has long been the most organized opposition group against the Damascus regime.

It's still outlawed in Syria after it was ruthlessly crushed by Assad's father, former President Hafez Assad, in 1982 when it declared war on the regime.

The Muslim Brotherhood has generally taken a more moderate position across the Arab world in recent years and is set to take power in Egypt and Tunisia after pro-democracy Arab Spring uprisings toppled longtime dictators in 2011.

Al-Qaida, for all its ferocity, has never succeeded in bringing down any of the Western-backed Arab regimes it has battled for years and it has lost ground to more moderate groupings like the Muslim Brotherhood.

But as Syria's badly fragmented, largely Sunni opposition has lost momentum in the face of an all-out security crackdown by Assad's regime and the Alawite military and security forces that have kept it in power since 1970, so al-Qaida has found opportunities to infiltrate the rebel ranks.

It's difficult to determine how successful the jihadist effort to muscle in on what it sees as an opportunity to take over the uprising and bring down what it considers an apostate regime and re-establish its revolutionary credentials at such a critical time in the Arab world.

But Arab intelligence sources say that non-Syrian jihadists, including battle-hardened Libyan fighters who helped topple Moammar Gadhafi, and veterans of the Iraq war, have made their way to Syria via Iraq, Lebanon and Jordan.

On Feb. 12, Ayman al-Zawahiri, who took over leadership of al-Qaida after Osama bin Laden was assassinated by U.S. Special Forces in Pakistan May 2, 2011, issued an 8-minute video entitled "Onward, Lions of Syria" in which he called on Muslims to aid the Syrian rebels.

Zawahiri, a veteran Egyptian jihadist who was widely seen as the eminence grise behind bin Laden, has long espoused the strategy of al-Qaida bringing down the pro-Western regimes in the Arab world, what he calls "the near enemy," rather than the "far enemy," the United States, that obsessed bin Laden.

Bin Laden's death, five months after the Arab Spring began, afforded Zawahiri an ideal opportunity to put his strategy to the test in Syria, strategically straddling many of the region's geopolitical fault lines.

At about this time, the Syrian regime was hit by a series of sophisticated bombings that targeted intelligence facilities and other symbols of its repressive power and were seen by many as the work of al-Qaida's veterans.

The United Nations and the United States have strived to avoid being dragged into the Syrian bloodbath, as they were in Libya, because of fears the revolution will degenerate into a sectarian conflict that will engulf neighboring Lebanon, Jordan and Iraq.

"While neither the domestic opponents of the Syrian regime nor the international stakeholders have an interest in seeing Syria collapse into sectarian conflict, jihadists want just that," the U.S. global security consultancy Stratfor observed.

"The jihadists could well succeed in sparking a regional sectarian conflict that would involve multiple state and non-state actors and would see Iran and Saudi Arabia locked in an intense proxy war."

The collapse of the Syrian state "would allow the jihadists a wide arena in which to operate, stretching from Lebanon to Iraq and putting them very close to Jordan, Israel and the Palestinian territories -- the best theater a jihadist could ask for," Stratfor said.