WASHINGTON — The senior State Department official who oversees diplomacy from South America to Canada is resigning as President Trump continues to limit asylum and block Central American migrants from entering the United States.

The official, Kimberly Breier, has been assistant secretary of state for Western Hemisphere affairs for less than a year. An expert in Latin American issues, she also has helped lead the Trump administration’s crackdown on Cuba, including restrictions that were announced in April to allow exiles to sue for property seized during Fidel Castro’s rule.

On Thursday morning, Secretary of State Mike Pompeo wrote on Twitter that Ms. Breier would be stepping down “After 2+ years of late nights & constant travel” in order “to spend more time with her family.”

“Kim’s expertise, counsel & passion ensured our nation seized opportunities & got results,” Mr. Pompeo wrote.