ANKARA: United States Vice President Joe Biden on Wednesday said Washington had made clear to pro-Kurdish forces in Syria not to cross west of the Euphrates River – a prospect that had alarmed Turkey. “We have made it absolutely clear that they (pro-Kurdish forces) must go back across the river and cannot – under no circumstances – get American support if they do not keep that commitment. Period,” Biden said at a news conference alongside Turkish Prime Minister Binali Yildirim.