Yemeni security officials say Shiite rebels in the capital have raided the homes of political opponents and local NGO workers, claiming they are affiliated with the Islamic State group and al-Qaida.

The officials, who are neutral in a conflict that has splintered the security forces, said Monday the raids began a day earlier. They spoke on condition of anonymity because they are not authorized to brief journalists.

Pro-government forces backed by Saudi-led airstrikes have driven the rebels, known as Houthis, from much of the country's south in recent weeks.

The officials said that last week the Houthis detained at least 20 people, one of whom works for the U.N., near the capital's presidential palace. Houthi officials could not immediately be reached for comment.