Al Qaeda’s affiliate inside Syria is now the best-equipped arm of the terror group in existence today, according to informal assessments by U.S. and Middle East intelligence agencies, a private sector analyst directly familiar with the information told CNN.

Concern about the Syrian al Qaeda-affiliated group Jabhat al-Nusra, also known as the al-Nusra Front, is at an all-time high, according to the analyst, with as many as 10,000 fighters and supporters inside Syria. The United States has designated al-Nusra Front as a terrorist group with links to al Qaeda in Iraq.

That assessment is shared by some Middle Eastern intelligence agencies that have long believed the United States is underestimating the Sunni-backed al Qaeda movement in the country, according to a Middle East source. It is also believed that Iran is running training camps inside Syria for Hezbollah and that other Iranian militia fighters are coming into the country to fight for the regime.