US officials' announcement of a possible new United Nations Security Council resolution on Syria’s chemical weapons has raised further hopes for US-Russia cooperation in ending Syria’s long civil war, but the road ahead is likely to be a slow one.

Secretary of State John Kerry did not definitively say that Washington and Moscow had reached an understanding on a resolution. Instead, he was cautious but clearly optimistic in stating that he and Russian Foreign Minister Sergey Lavrov “talked about the UN resolution and indeed I believe reached an agreement that should try to see that resolution voted shortly.” As of this writing, whether Lavrov also believes they reached an agreement is not immediately clear. Interestingly, official Russian media reports of the possible deal quote only US and Western sources in describing it.

Kerry described the draft resolution, which apparently focuses on investigating chemical weapons use in Syria, as establishing “a process of accountability which has been missing.” In no small part, this process has been missing precisely because the United States and Russia have disagreed over whether and how to go about it. Last year, Russia (and China) vetoed a broader UN resolution seeking to refer alleged war crimes in Syria to the International Criminal Court.

One problem is that while US officials clearly seek to use any investigative process to apply further pressure to Syrian President Bashar al-Assad and his government, Moscow has been reluctant to do this — and, in fact, believes that opposition fighters have also been using chemical weapons. Senior Russian officials and parliamentarians are also suspicious that Washington could eventually use an investigation to justify military action against the Syrian regime. If the Security Council passes a resolution, Moscow is likely to seek to limit its scope to prevent this.