USAID and its contractors went to extensive lengths to conceal Washington's ties to the project, according to interviews and documents obtained by the AP. They set up front companies in Spain and the Cayman Islands to hide the money trail, and recruited CEOs without telling them they would be working on a U.S. taxpayer-funded project.

USAID said in a statement that it is "proud of its work in Cuba to provide basic humanitarian assistance, promote human rights and fundamental freedoms, and to help information flow more freely to the Cuban people," whom it said "have lived under an authoritarian regime" for 50 years. The agency said its work was found to be "consistent with U.S. law."

Sen. Patrick Leahy, D-Vt., chairman of the Appropriations Committee's State Department and foreign operations subcommittee, said the ZunZuneo revelations were "troubling".

"There is the risk to young, unsuspecting Cuban cellphone users who had no idea this was a U.S. government-funded activity," he said. "There is the clandestine nature of the program that was not disclosed to the appropriations subcommittee with oversight responsibility.

"There is also the fact that it was apparently activated shortly after Alan Gross, a USAID subcontractor who was sent to Cuba to help provide citizens access to the Internet, was arrested."

The network discontinued use in 2012.