The Obama administration has begun to see Jabhat al-Nusra, al-Qaeda’s affiliate in Syria, as a global threat that could eventually rival the Islamic State, echoing a Russian argument that it has long resisted.

A new U.S. proposal to coordinate counterterrorism operations in Syria with Russia, discussed by President Obama last week with Russian President Vladi­mir Putin, is partly designed to stop Moscow’s Syrian government ally from bombing civilians and U.S.-backed moderate opposition ­forces.

But stopping al-Nusra, which has been one of the main beneficiaries of the ongoing Syrian civil conflict, appears to have become an almost equally important goal. The proposed deal would start with coordinated U.S. and Russian strikes against al-Nusra.

The group’s capacity is growing, and it is “the largest al-Qaeda affiliate now in the world,” Brett McGurk, the administration’s envoy to the global coalition against the Islamic State, said this week.