Paul Oquist, a U.S.-born academic who became a close adviser to Nicaraguan President Daniel Ortega and drew U.S. financial sanctions has died in the Central American nation of undisclosed causes, the president's office said on Tuesday.

Oquist, who was born in 1943, had served in a variety of administrative positions under Ortega's Sandinista governments during the 1980s and again after he returned to power in 2007. During the 1990s, he had worked in a series of U.N. posts.

Oquist most recently was a political adviser and in charge of the stalled, Chinese-financed project to build a canal across Nicaragua to rival the Panama Canal. He also published a book last year on the global environment, titled “Equilibra."

Born in Oak Park, Illinois, he attended schools in the Los Angeles area and graduated from the University of California, Los Angeles, in 1965. He later studied in Santiago, Chile, obtained a doctorate in political science from the University of California, Berkeley, and spent time teaching in Colombia — the subject of his doctoral thesis.

His public defense of the Ortega government's crackdown on opponents earned him the hostility of the Trump administration, which last year included him on a list of more than two dozen Nicaraguan officials subject to financial sanctions.

He was married to a Nicaraguan and was naturalized in the Central American country.

“Paul Oquist Kelly served the people, the families, all Nicaraguans with love, faithfulness, commitment and untiring bravery," Ortega and first lady Rosario Murillo said in a message announcing his death.