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WASHINGTON, Oct 18 (Reuters) - President Donald Trump on Thursday said he would deploy the U.S. military and close the southern border if Mexico did not move to halt large groups of migrants headed for the United States from Guatemala, Honduras and El Salvador.

"I must, in the strongest of terms, ask Mexico to stop this onslaught - and if unable to do so I will call up the U.S. Military and CLOSE OUR SOUTHERN BORDER!" Trump wrote on Twitter. (Reporting by Susan Heavey and Doina Chiacu; Editing by Bernadette Baum)

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