By AHMED AL-HAJ Associated Press

Shiite rebels in Yemen's capital have raided dozens of homes of political opponents and local NGO workers, claiming they are affiliated with the Islamic State group and al-Qaida, security officials said Monday.

The officials, who are neutral in a conflict that has splintered the security forces, said the raids began a day earlier.

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, but the rebels still hold the capital, Sanaa, which they seized nearly a year ago.

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.

Also Monday, mortar rounds fired by the rebels killed four civilians and wounded six in Yemen's third largest city of Taiz, medical officials and witnesses said.

The exiled Yemeni government in Saudi Arabia declared Taiz a disaster zone last week. Since then, the city's al-Radwah hospital has stopped admitting patients due to a severe lack of medical resources, officials at the hospital told the Associated Press, leaving Taiz with only six working hospitals out of 21.

All officials and witnesses requested anonymity because they are not authorized to brief journalists or for fear of reprisals.

Yemen's conflict pits the Iran-supported Houthis and allied army units against southern separatists, local and tribal militias, Islamic militants and forces loyal to exiled President Abed Rabbo Mansour Hadi. A Saudi-led and U.S.-backed coalition has been striking the rebels and their allies since March.

The conflict has killed some 2,000 civilians, according to the United Nations.