BAGHDAD — The lone Syrian rebel group with an explicit stamp of approval from Al Qaeda has become one of the uprising’s most effective fighting forces, posing a stark challenge to the United States and other countries that want to support the rebels but not Islamic extremists.
Money flows to the group, the Nusra Front, from like-minded donors abroad. Its fighters, a small minority of the rebels, have the boldness and skill to storm fortified positions and lead other battalions to capture military bases and oil fields. As their successes mount, they gather more weapons and attract more fighters.
The group is a direct offshoot of Al Qaeda in Iraq, Iraqi officials and former Iraqi insurgents say, which has contributed veteran fighters and weapons.
“This is just a simple way of returning the favor to our Syrian brothers that fought with us on the lands of Iraq,’’ said an insurgent veteran of Al Qaeda in Iraqi, who said he helped lead Nusra Front’s efforts in Syria. The United States, sensing that time may be running out for Syria’s president, Bashar Assad, hopes to isolate the group to prevent it from inheriting Syria or fighting on after Assad’s fall to pursue its goal of an Islamic state.
As the United States pushes the Syrian opposition to organize a viable alternative government, it plans to blacklist the Nusra Front as a terrorist organization, making it illegal for Americans to have financial dealings with the group and most likely prompting similar sanctions from Europe.
The hope is to remove one of the biggest obstacles to increasing Western support for the rebellion: the fear that money and arms could flow to a jihadi group that could further destabilize Syria and harm Western interests.
When rebel commanders met Friday in Turkey to form a unified command structure at the behest of the United States and its allies, jihadi groups were not invited.
The Nusra Front’s ally, Al Qaeda in Iraq, is the Sunni insurgent group that killed numerous US troops in Iraq and sowed widespread sectarian strife with suicide bombings against Shi’ites and other religious and ideological opponents.
The Iraqi group played an active role in founding the Nusra Front and provides it with money, expertise, and fighters, said Major Faisal al-Issawi, an Iraqi security official who tracks jihadi activities in Iraq’s Anbar Province.
But blacklisting the Nusra Front could backfire. It would pit the United States against some of the best fighters in the insurgency that it aims to support. While some Syrian rebels fear the group’s growing power, others work closely with it and admire it — or, at least, its military achievements — and are loath to end their cooperation.
The United States has been reluctant to supply weapons to rebels that could end up in the hands of anti-Western jihadis, as did weapons that Qatar supplied to Libyan rebels with American approval. Critics of the Obama administration’s Syria policy counter that its failure to support the rebels helped create the opening that Islamic militants have seized in Syria.
The Nusra Front’s appeals to Syrian fighters seem to be working. At a recent meeting in Damascus, Abu Hussein al-Afghani, a veteran of insurgencies in Afghanistan, Iraq, and Libya, addressed frustrated young rebels. They lacked money, weapons, and training, so they listened attentively.
He told them he was a leader of Al Qaeda in Iraq, now working with an Al Qaeda branch in Syria, and by joining him, they could make their mark. One fighter recalled his resonant question: ‘‘Who is hearing your voice today?’’
On Friday, demonstrators in several Syrian cities raised banners with slogans like, ‘‘No to American intervention, for we are all Jebhat al-Nusra,’’ referring to the group’s full name, Ansar al-Jebhat al-Nusra li-Ahl al-Sham, or Supporters of the Front for Victory of the People of Syria. One rebel battalion, the Ahrar, or Free Men, asked on its Facebook page why the United States did not blacklist Assad’s ‘‘terrorist’’ militias.
Another jihadist faction, the Sahaba Army in the Levant, even congratulated the group on the ‘‘great honor’’ of being deemed terrorists by the United States.
Even antigovernment activists who are wary of the group — some deride it as ‘‘the Taliban’’ — said the blacklisting would be ineffective and worsen strife within the uprising. To isolate the group, they say, the United States should support mainstream rebel military councils and Syrian civil society, like the committees that have sprung up to run rebel-held villages.
The Nusra Front is the only Syrian rebel group explicitly endorsed by Al Qaeda in online forums, the report said.
The group gained prominence with suicide bombings in Damascus and Aleppo in early 2012 that targeted government buildings but caused heavy civilian casualties. It was the first Syrian insurgent organization to claim responsibility for suicide and car bomb attacks that killed civilians.
Many of its members — Syrians, Iraqis, and a few from other countries — fought in Iraq, where the Syrian government helped funnel jihadis to battle the American occupation.
In Iraq’s Diyala Province, a former member of Al Qaeda in Iraq said that a leader and many members of the group were fighting in Syria under the Nusra Front’s banner.