Four Americans are being held by Shiite Houthi rebels in Yemen who toppled the U.S.-backed government earlier this year, a senior defense official confirmed Sunday. 

The official who confirmed that the Americans were being held did not have any more information, but the department released a statement earlier Sunday that said it was "doing everything we can to get these individuals released." The statement added that the department would not release personal information about those being held due to privacy concerns. 

The Washington Post, citing unnamed sources, first reported Sunday that the Americans were being held and that attempts to free them have failed. The four are believed to be imprisoned in the Yemen capital of Sanaa, which Saudi Arabia has repeatedly bombed in a campaign to oust the Houthi rebels from power, the newspaper reported.

The Houthis had cleared one of the prisoners for release, but the Post report says other members of the rebel forces reversed the decision.

Three of the four prisoners held private sector jobs and fourth holds dual American-Yemeni citizenship. None is a U.S. government employee, according to the Post.

U.S. officials and relatives requested that the Post withhold details about the four citing safety concerns.

Another American, Sharif Mobley, is also being held in Houthi custody. He’s been held for more than five years on terrorism-related charges brought by the previous government.

The Post report said those most recently detained are among dozens of Americans who were unable to leave Yemen or who chose to remain in the country after the U.S. closed its embassy.

Fox News' Jacqueline Pham and The Associated Press contributed to this report.