Military officials and Shiite rebels say Saudi-backed Yemeni troops have failed to take control of Aden's downtown district of Tawahi and the presidential palace after intense fighting overnight.
Military officials say they underestimated the numbers of rebel Houthis fighters in Tawahi on Saturday, adding that they will regroup and launch another offensive.
The Yemeni government, now largely in exile in Saudi Arabia, had said they were consolidating control of Aden with only a few "terrorist pockets" of Houthis remaining on Friday. That followed a major offensive to retake the city last week.
A Houthi official said they are trying to regain full control of Aden, vowing to fight to the death.
The officials spoke on condition of anonymity because they were not authorized to speak to reporters.