Officials say 20 people died in clashes in Yemen's Marib province and the city of Taiz between Shiite Houthi rebels and pro-government forces who are backed by airstrikes from a Saudi-led coalition.

Medical sources in Marib say clashes there killed nine rebels and seven anti-Houthi tribesmen.

Medical and security officials in Taiz say Houthi shelling killed four civilians.

Security officials in the southern port city of Aden say clashes also raged north of the city.

All officials spoke on condition of anonymity because they were not authorized to talk to reporters.

The fighting in Yemen pits the Houthis and troops loyal to former President Ali Abdullah Saleh against southern separatists, local and tribal militias, Sunni Islamic militants and loyalists of exiled President Abed Rabbo Mansour Hadi.