Fighters from the militant group have teamed up with pro-government militias as well as UAE soldiers on the frontlines of the war.
The revelations came from a documentary filmmaker who was filming with the fighters just a few miles from Yemen's besieged Taiz, the BBC reported.
More than 6,000 people have been killed in the impoverished Arabian Peninsula state, about half of them civilians, since the Saudi-led coalition launched an air campaign to combat Houthi rebels across the country ten months ago.
But the latest pending battle is focused on the besieged northern city, Taiz – Yemen's third largest with over 200,000 residents.
Saudi Arabian documentary filmmaker, Safa al-Ahmad, who filmed Houthi rebels at the height of their movement in September 2014, was just a few miles from the Taiz frontlines when she said she was told not to film a group seen participating with the coalition because they were angered by the presence of a woman.
The group, she was told, was Ansar al-Sharia, an al-Qaeda affiliate in the Araban Peninsula (AQAP).
Fears that power vacuums and a deteriorating security crisis in parts of southern Yemen have allowed extremist groups - such as al-Qaeda and the Islamic State group to proliferate.
Al-Qaeda militants captured Ahwar on Saturday, adding yet another southern town to the list of territories under their control.
Three pro-government fighters were captured by the militants and had their throats slit during the operation.
Despite this, numerous reports revealing co-operation between militants and government troops have emerged since the aerial campaign began in March.