The clashes, which resumed early today, came as loyalist forces pressed an offensive to retake third city Taez in the southwest of Yemen which has been under siege for months by Huthi rebels.
The fighting in Aden raged in the jihadist stronghold of Mansura, a residential area which loyalist forces backed by aircraft from a Saudi-led coalition have been trying to recapture since yesterday.
Coalition fighter jets and Apache helicopters carried out air strikes overnight that hit at least three vehicles and a local council office occupied by the jihadists, security sources said.
Dozens of gunmen in balaclavas carrying the al-Qaeda flag deployed to push back police trying to enter the central Aden neighbourhood, witnesses said.
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The police said in a statement that fighting against the "armed terrorist gangs in Mansura will continue to ensure the safety of residents" in Yemen's main southern city.
Security sources estimate that around 300 heavily armed al-Qaeda fighters are entrenched in Mansura.
Al-Qaeda and the Islamic State group have taken advantage of the conflict between Iran-backed Huthi insurgents and pro-government forces to reinforce their presence in the south, including in Aden.
Coalition aircraft provided support and hit a military convoy that was trying to bring reinforcements to the rebels, the sources said.
At least 94 people have been killed in the offensive since Friday, including 24 rebels, nine loyalist forces and four civilians, the sources added.
Officials are hoping to break the siege in order to deliver desperately needed humanitarian aid to the nearly 200,000 residents trapped in Taez.
More than 6,100 people have died, half of them civilians since the coalition launched air strikes against the Shiite rebels and their allies in March 2015, according to the UN.