Russia Promises Reprisals To U.K. As White House Calls Out Moscow Over Poison Attack

Updated at 9:50 a.m. ET

Russia says it will retaliate against Britain's recently announced sanctions, saying that President Vladimir Putin will soon decide the best way to respond to the U.K.'s expulsion of 23 Russian diplomats. It's the latest escalation in the clash between the two nations over the use of a military-grade nerve agent against a former Russian spy who is now a British citizen.

"A final decision [on retaliatory measures] will, of course, be made by the president of the Russian Federation," presidential spokesman Dmitry Peskov said, according to state-run Tass media. "There are no doubts that he will choose the variant that best of all corresponds to the interests of the Russian Federation."

Russian Foreign Minister Sergey Lavrov said, "The response will