US Secretary of State Hillary Clinton said on Saturday that it had not been possible to effectively work with Russia on a UN resolution backed by the West and the Arab League calling for Syrian President Bashar Assad to step down, which the United Nations Security Council is scheduled to vote upon. "I thought that there might be some ways to bridge, even at this last moment, a few of the concerns that the Russians had. I offered to work in a constructive manner to do so. That has not been possible," Clinton told reporters at the Munich Security Conference.