The Houthis, Iran-backed rebels who overthrew the government of Yemen, have released one of four Americans held captive, according to CNN, relaying a report from Oman’s official news agency.

According to the report, Oman’s Sultan Qaboos bin Said ordered his government to “help” American officials “find the missing citizen in Yemen.”

It remains unclear where the other Americans are being held or why they were seized. Nothing is known about their current condition, although there is said to be no indication they were harmed. Efforts by various third parties to secure their release are under way, although the U.S. government has no direct line of communication to the rebels. According to the New York Timesthose third-party intermediaries include China, Russia, and Iran.

“At least one captive is believed to be a dual U.S.-Yemeni national,” CNN reports. “They are among dozens of Americans who chose to stay in Yemen or were unable to leave the country after the U.S. closed its embassy in February and evacuated its personnel.”

News of the four abductions was first broken by the Washington Post on Sunday. This report said the four prisoners were being held at “a prison in Sanaa, the Yemeni capital, which has been bombed repeatedly as part of an air campaign led by Saudi Arabia aimed at dislodging the Houthis from power.” Later reports have questioned whether the remaining prisoners are being held in the same place.

According to the Post, early efforts to secure the release of the prisoners failed, with one of them initially cleared for release by the Houthis before they reversed their decision. He was reportedly imprisoned for overstaying his visa, and began behaving “erratically” in captivity — at one point stripping himself naked.  It’s not clear if this is the same individual whose eventual release CNN reported.

According to the Washington Post report, none of the four is an employee of the U.S. government. Further details about the prisoners have been withheld out of concern for their privacy and safety.