Five countries will provide additional air defense systems for Ukraine in the coming months.
U.S. officials are asking troops to be more vigilant and keep a lower profile due to a combination of present threats.
During the call, the two discussed "maintaining lines of communication" a day after Russia promised retaliation for a Ukrainian strike on Crimea.
The Army is naming its short-range air defense system after Sgt. Mitchell William Stout, who saved lives in Vietnam.
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