Al-Qaeda suspects freed 21 policemen they captured during a deadly attack against security personnel in southern Yemen last week, a security official said Tuesday.

"Al-Qaeda militants released the 21 captured policemen following tribal mediation," the official told AFP.

A tribal source confirmed the release in Mahfad, a rugged mountainous region between the southern provinces of Abyan and Shabwa.

He said the captors "received nothing in return."

The militants captured the policemen in a Friday attack at a special forces camp in Maifaa, in Shabwa province.

The attack, in which eight policemen died, was one of three spectacular assaults that killed 56 security personnel.

The deadliest one was on an army camp responsible for ensuring security at Shabwa oilfields, and the third targeted an army checkpoint in Al-Nushaima area.

Troops foiled a fourth attack using a bomb-laden vehicle that was heading towards the key Balhaf gas terminal.

Security was beefed up in Balhaf the following day, and witnesses reported Tuesday that Yemeni jets were still flying over the area without carrying out any raids.

Authorities have blamed the attacks on Al-Qaeda in the Arabian Peninsula, still active in Yemen's lawless south and east despite repeated army offensives to break its back.

The network has not claimed Friday's attacks.

AQAP took advantage of a decline in central government control and seized large swathes of territory during a 2011 uprising that forced president Ali Abdullah Saleh from power. The government has since retaken much of the lost territory.

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