With al-Qaeda’s Nusra Front taking over more and more territory in Syria, and reportedly preparing to establish an independent “emirate” that would mirror the government set up by ISIS, Russia today issued a statement calling for joint operations against the Islamists with the United States.

Both the US and Russia are engaged in airstrikes against ISIS in Syria, and both have at times launched strikes against al-Qaeda’s forces there as well. US officials, however, didn’t respond kindly to the idea of joint operations against al-Qaeda.

“We do not collaborate or cooperate with the Russians,” insisted Pentagon spokesman Capt. Jeff Davis, who added that the US has “different military objectives” in Syria than the Russians do, and that the US is focused on “defeating ISIS.”

The US and Russia have been conducting bilateral negotiations on a plan to end the Syrian Civil War after five years, and Russia couched today’s proposal as a way to remove a major obstacle to the peace, al-Qaeda’s stranglehold on much of northwest Syria. US officials, however, seem determined to reject any Russian plan out of hand, which likely explains why the months of negotiations have just amounted to intermittent US statements of condemnation.