Four U.S. citizens were sentenced in federal court for their roles in a failed attempt to overthrow the government in the West African nation of Gambia, the U.S. attorney's office said Thursday.

The men were sentenced for conspiring to violate the Neutrality Act, which makes it illegal to take military action against a country with which the United States is "at peace." The charges stemmed from a Dec. 30, 2014, coup attempt in the former British colony, which came as longtime President Yahya Jammeh was away.

"These defendants conspired to overthrow a foreign government," U.S. Attorney Andrew Luger said in a statement. "Regardless of the legitimacy of their personal and emotional connections to The Gambia, these men placed countless innocents in harm's way when they engaged in a brazen and fatally flawed attempt at regime change."

Cherno Njie, 58, of Lakeway, Texas, was sentenced to a year and a day in prison. Prosecutors say Njie was a financier and would have served as the interim leader of Gambia had the coup succeeded.

Alagie Barrow, 43, of Lavergne, Tennessee, and Banke Manneh, 43, of Jonesboro, Georgia, were each sentenced to six months in prison. Papa Faal, 47, of Brooklyn Park, Minnesota, a former member of the U.S. military, was sentenced to time served.

Faal, a dual citizen of the U.S. and Gambia, admitted in court that he participated in the attack on Gambia's State House. Three other members of the conspiracy were killed, the U.S. attorney's office said.

According to the defendants' guilty pleas and court documents, the coup plotting began in at least 2013. Prosecutors say Njie, Manneh and Barrow led the effort to research, plan, supply and execute the coup.

The defendants planned the coup by phone, email or face-to-face at Njie's home in Texas, court documents said. According to an FBI affidavit, a search of Njie's home revealed a spreadsheet that suggested Barrow, a former member of the Tennessee Army National Guard, may have received more than $125,000 to support the operation. At Barrow's home, authorities found a book about planning a coup.