The captain and chief engineer were taken on October 23 when gunmen attacked the U.S.-flagged C-Retriever, a 222-foot (67 metre) vessel owned by U.S. marine transport group Edison Chouest Offshore.
“We welcome the release of the two U.S. citizens who were kidnapped from the M/V C-Retriever. For privacy reasons, we will not provide any additional information,” a State Department official said in a statement.
Pirate attacks off Nigeria’s coast have jumped by a third this year as ships passing through West Africa’s Gulf of Guinea, a major commodities route, have come under threat from gangs wanting to snatch cargoes and crews.
The White House said last month it was increasingly concerned about the rise in piracy off West Africa.
Unlike the waters off Somalia on the east coast of Africa, through which ships now speed with armed guards on board, many vessels have to anchor to do business off West African countries with little protection.
This makes them targets for criminals and raises insurance costs. Kidnapped sailors and oil workers taken in Nigerian waters are usually released after a ransom is paid.
“It is the policy of the United States not to pay ransom or encourage the payment of ransom money,” the State Department statement said.