FLDS/LDS Prophet Brigham Young made this statement in 1846: "I ... warned those who lied and stole and followed Israel that they would have their heads cut off, for that was the law of God and it should be executed" ("Manuscript History of Brigham Young," December 20, 1846, typed copy; original in LDS church archives).
"If any miserable scoundrels come here, cut their throats." - From red hot blood atonement sermon by Brigham Young, Journal of Discourses, Vol. II., page 311. At the conclusion of the injunction to "cut their throats, " "all the people said 'amen!' "
On the other hand, there are some other groups unfriendly to the US who are actually lopping off heads, some in the Middle East and some on our southern border.