CAIRO — Several American citizens are being detained in Yemen by the Houthis, a Shiite rebel group that controls the capital and parts of the country, a United States official said Sunday.

The official did not immediately provide information about the Americans’ identities or details about their cases. One was detained about two weeks ago, according to family members.

The detainees were believed to be held in Sana, the capital, raising concerns about their safety. Security installations controlled by the Houthis in the city have come under repeated aerial bombardment by a military coalition led by Saudi Arabia.

The Washington Post, citing unidentified officials, reported Friday that at least four Americans were believed to be in Houthi custody in Sana. It said none worked for the United States government, and one was believed to hold dual Yemeni and American citizenship.