"This is a chess game and the Russians are ratcheting up the pressure," a U.S. official told VOA on the condition of anonymity given the sensitivity of the situation. "They're playing dirty," the official added. "We need to think two or three steps ahead."

Russia, long an ally of Syrian President Bashar al-Assad, has warned a military conflict could erupt if the U.S. and its Western allies take action in Syria.

"We hope that ... the U.S. and their allies will refrain from military action against a sovereign state," Russian Ambassador to the U.N. Vassily Nebenzia said Friday.

Also Friday, Moscow alleged it had "proof that testifies to the direct participation of Britain" in staging the chemical attack in Douma.

Britain pressured the White Helmets, volunteers and activists who serve as first responders in rebel-held areas, to stage the attack, Defense Ministry spokesman Igor Konashenkov said.

Britain called the allegation a "blatant lie."

美国官员表示“高度确信”叙利亚发动了上星期东古塔杜马镇的化学武器袭击案，并且表示西方会做出反应，而且各种选项都不排除。

虽然美国总统川普本星期早些时候发推表示可能立刻进行导弹打击，但是白宫、国务院和五角大楼用词都一直比较谨慎，强调需要找齐针对叙利亚总统阿萨德政府的铁证。

到了星期五傍晚，有迹象显示这样的证据正在汇集起来。

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