Leaders of Syria's largest rebel faction and top commanders for al Qaeda's Iraqi and Syrian factions have reached a peace deal, agreeing to come together to battle the growing Iranian presence in the country.

Senior leaders from the Free Syrian Army (FSA) and Islamic State of Iraq and al-Sham (ISIS), a teaming of al Qaeda's Iraqi cell and affiliated Syrian militant groups, agreed to the deal after a meeting in Aleppo over the weekend.

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"ISIS and FSA infighting ceased mostly after a meeting of commanders . . . led all parties to decide to focus their efforts" against forces loyal to Syrian President Bashar Assad and his Iranian backers, Syrian Support Group spokesman Dan Layman told The Hill on Monday.

As a result, both groups have launched "joint counteroffensives" against Hezbollah and Iranian military positions in and around Aleppo, according to Layman, whose D.C.-based organization backs the secular wing of the Syrian opposition.

Iran and Russia have been the biggest international backers of the Assad regime since war broke out in the country three years ago.

FSA and ISIS counterattacks have been focused in regime and Iranian-controlled portions of the city, specifically in Rashadeen and the Maarat Arteeq mountains along Aleppo's northern border, according to Layman citing rebel sources in country.

Earlier this month, a top commander with Iran's Revolutionary Guard Corps (IRGC) was reportedly killed inside Syria, shedding more light into the extent of Tehran's military involvement in the over two-year civil war there.

IRGC commander Mohammad Jamali was killed during an attack in Syria, according to the state-run Iranian news outlet Mehr.

The report blamed "terrorists" inside Syria for Jamali's death, calling the military officer a "martyr" who died defending Sayyidah Zaynab Mosque in the Syrian capitol of Damascus.

That said, Tehran has denied that Jamali's presence inside Syria was a sign that Iran's military is increasing its supporting role to government forces loyal to embattled Syrian President Bashar Assad.

However, Layman's group claims a 4,000-man force of Hezbollah fighters and members of the Iraqi Shia Mahdi Army on on the ground in Syria, along with an estimated 1,000 IRCG troops sent by Tehran.

The pact between the moderate and al Qaeda-linked factions within the opposition comes amid increased concern from Washington over the terror groups increasing influence among Syrian rebel forces.

The teaming of al Qaeda's Syrian and Iraqi factions has developed into "a major emerging threat to Iraqi stability ... and to us," a senior administration official told reporters in October.

"It is a fact now that al Qaeda has a presence in Western Iraq" extending into Syria, "that Iraqi forces are unable to target," the official added at the time.

But the al Qaeda's increased presence in Syria has raised tensions within the opposition, leading to open fighting between the group's fighters and the moderate rebel forces.

The Sunni-dominated Syrian opposition is beginning to push back against al Qaeda's influence in Syria, Director of National Intelligence James Clapper told Congress in April.

"There are increasing indications though that the moderate Islamists are . . . not comfortable" with AQI and al Nusra joining forces, attempting to co-opt the opposition to establish al Qaeda in Syria, Clapper told House Intelligence Committee members.

"There are indications of divisiveness among the Sunni opposition groups," he added at the time. "So how that will play out, [it is] hard to say. That's something we're watching carefully."