By Robin Emmott and Sabine Siebold BRUSSELS (Reuters) -The European Union is ready to impose “never-seen-before” economic sanctions on Russia if it attacks Ukraine, Denmark said on Monday, and EU foreign ministers said they would send a unified warning to Moscow. East-West tensions have risen since Russia massed troops near Ukraine’s border, with Western countries fearing Moscow is preparing an invasion. Russia denies such plans. Divergent interests in the 27-nation EU could hinder efforts to agree a joint position, and the EU is sidelined by direct Russia-U.S. talks, but ministers said it was…