"The U.S. government is suspending part of the foreign assistance programs benefiting the Gabonese government until we assess the unconstitutional interference by members of this country's military," Blinken said in a statement.
The United States urged Gabon's military to "maintain civilian rule" and expressed concern after the coup that toppled the country's president in August, following an election that raised doubts about its fairness.
State Department spokesman Matthew Miller said in a statement: "We urge those in charge to release members of the government and their families, ensure their safety and maintain civilian rule."
"The United States is deeply concerned about the development of events in Gabon. We remain strongly opposed to military takeover or an unconstitutional transfer of power."
Miller's statement was not the first U.S. reaction to the coup in Gabon, with the White House earlier saying it was "closely following" the situation in the African country.