The high-level talks on Ukraine that are set to begin here on Thursday have emerged as a pivotal test of Russia ’s intentions in the region before the United States and European nations decide whether to impose additional economic sanctions on Moscow, American officials said on Wednesday. “The idea here is that they would stop aiding and abetting and supporting these separatists and that they would pull their troops back from the border,” said a senior State Department official, referring to Western charges that Russia is behind the separatist protests in eastern Ukraine. “If Russia does not take this opportunity to de-escalate, the costs are going to go up,” the official said. Secretary of State John Kerry will participate in the four-way meeting, which is to be held in a luxury hotel here, along with the Russian foreign minister, Sergey V. Lavrov; Ukraine’s acting foreign minister, Andrii […]