With the Syrian military continuing its offensive in Aleppo, the Obama Administration today announced that it holds Russia fully responsible for the fighting there, and said it was issuing an ultimatum demanding that Russia “immediately” end the offensive.

State Department officials ducked the question of what “immediately” was, and warned that the US would suspend all plans for potential coordinated strikes in Syria unless Russia complies with the demand. The US had already reneged on the promised coordinated strikes from the last ceasefire, so Russia likely wasn’t counting on this to ever happen at any rate.

A ceasefire two weeks ago was supposed to last for seven days, leading to joint US-Russia strikes on the Nusra Front in Aleppo. Five days in, the US attacked a Syrian Army base, and Syria withdrew from the ceasefire on the seventh day, attacking Nusra targets in Aleppo. Despite the ceasefire lasting seven days, however, the US made no move to start coordination with Russia, and instead repeatedly condemned them in the last couple of days.

Russian officials shrugged off the threat, with the Defense Ministry saying that Russia remains willing to work with the US whenever they are ready to do so. The State Department claimed to have discussed “non-diplomatic responses” to Russia in Syria, but declined to offer details on what that means, though they clear meant to imply that military options are on the table.

The US has struggled with its stance on the Nusra Front throughout the Syrian Civil War, with the CIA arming them in rather thinly veiled shipments to “moderates,” and the Pentagon attacking them as an al-Qaeda affiliate early in the US air war. In recent months, however, US officials have held out the prospect of joint attacks with Russia against Nusra repeatedly, while at the same time loudly condemning Russia and Syria for any unilateral moves against Nusra.