Citing unnamed sources, The Washington Post said attempts to free the Americans have failed. The Americans are believed to be imprisoned in the capital Sanaa, which Saudi Arabia has repeatedly bombed in a campaign to oust the rebels, known as Houthis, from power, the report said.
"We have seen reports that several U.S. citizens have recently been detained in Yemen," the State Department said in a statement. "We are doing everything we can to get these individuals released.
"Due to privacy considerations, we do not have any further personal details or information to share," the agency said. "The protection of U.S. citizens abroad is a top priority." The State Department did not provide an exact number of U.S. prisoners detained.
The Houthis had cleared one of the prisoners for release, but the Post report said members of the Houthi rebellion reversed that decision.
Three of the prisoners held private sector jobs, and the fourth holds dual U.S.-Yemeni citizenship. None is a U.S. government employee, the report said.
The Post report said the newspaper is withholding details about the four, at the request of relatives and U.S. officials, who cited safety concerns.
One more American is being held in Yemen. Sharif Mobley is also in Houthi custody. He's been held for more than five years on terrorism-related charges brought by the previous government; his capture has been reported previously.
Few details were available. The U.S. has limited contact with the Houthis.
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.
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