俄罗斯周三暂停了同美国在核能以及与能源相关研究的一个三年合作协议，这一最新举动标志着两国关系的继续恶化。
一位不愿意透露姓名的美国资深官员对美国之音说：“坦率地讲，这一情况令人担忧。”
俄罗斯总统普京周一还签署了一道命令，暂停了一项与美国达成的处理武器级钚的协议，理由是华盛顿采取了“不友善的行动”，意指以美国为首的国家对莫斯科在乌克兰的行动进行了制裁。
美国国务院发言人托纳在周三的每日通报会上说，废弃钚协议是“一个真正的悲剧，因为在这些领域内，我们以前的合作是成功的。”
由于针对平民目标的袭击持续不断，美国中断了和俄罗斯就叙利亚停火的直接会谈。美国政府宣称已经对莫斯科失去耐心。但美国国务卿克里和俄罗斯外长拉夫罗夫周三再次就叙利亚问题进行了交谈。
华盛顿和莫斯科的外交官员均表示，美国主动提出了电话交谈的要求，交谈内容还涉及乌克兰以及朝鲜问题。
Russia on Wednesday suspended a three-year-old agreement with the United States on cooperation on nuclear and energy-related research — the latest move signifying a deteriorating bilateral relationship.
"It's frankly concerning," a senior U.S. official told VOA on condition he not be named.
Russian President Vladimir Putin on Monday also signed a decree suspending an agreement with the U.S. on disposing weapons-grade plutonium, citing "unfriendly actions" by Washington — a reference to U.S.-led sanctions on Moscow for its actions in Ukraine.
Nullifying the plutonium pact is "a real tragedy because these are areas where we have successfully cooperated in the past," State Department spokesman Mark Toner said during Wednesday's daily briefing.
The United States has halted Syria cease-fire direct talks with Russia amid continuing military attacks against civilian targets, with the U.S. administration declaring its patience at an end with Moscow. However, Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov spoke again Wednesday about Syria.
Diplomats in both Washington and Moscow say the United States requested the call, which also covered the situations in Ukraine and North Korea.
