The al-Nusra Front, an Islamist faction of Syrian rebels described in recent reports as a “key” part of an eventual rebel conquest of the nation, is going to be added to the US State Department’s list of foreign terrorist organizations, according to diplomats.

Al-Nusra, an al-Qaeda-styled organization which has been responsible for myriad suicide bombings and a sustained campaign of attacks and assassinations on Syrian media that it perceives as insufficiently pro-rebel, has long been kept at arm’s length by other rebels, fearing the taint of the group’s decidedly terrorist strategy.

At the same time, many of those groups now concede that al-Nusra’s support is virtually obligatory for any major rebel moves, and the US estimates it atabout 9% of the overall rebel fighting force.

The group is upset at the planned designation, but does not dispute their tactics. Rather, they argue that there hasn’t been any specific evidence to prove their direct link to al-Qaeda, which is true enough but given the groups’ common ideology and tactics likely beside the point.

The timing of the move is somewhat surprising, coming as the Obama Administration is nearing plans to begin directly arming rebels. Conceding one of the likely beneficiaries of the arms as a terrorist organization beforehand will likely complicate efforts, and leave the US on the defensive about the policy in general.