Suspected Al-Qaeda gunmen killed five south Yemen soldier in Abyan province on Monday, in the terror group's biggest attack in the region for months, a secessionist security official said.

The five members of the Security Belt  force, which is dominated by the Southern Transitional Council (STC), were killed at dawn on the outskirts of Lawdar city, the official told AFP.

"It was gunmen believed to be from Al-Qaeda who launched the attack and managed to escape," he said, speaking on condition of anonymity.

A medic in Lawdar confirmed the death toll, while Al-Qaeda has yet to issue any statements on the attack.

Al-Qaeda in the Arabian Peninsula has thrived in the chaos of Yemen's civil war between an internationally recognised government that is supported by a Saudi-led coalition and the Iran-backed Shiite Huthi rebels.

The United States, which considers AQAP the terror group's most dangerous branch, has carried out a campaign of drone strikes against its leaders for the past two decades.

Monday's attack was the biggest in southern Yemen since August, when Al-Qaeda killed a dentist in Al-Bayda accused of guiding US drone strikes against its militants and later that month blew up the medical centre in which he worked.

Security Belt forces played a decisive role in fighting against Al-Qaeda and the Islamic State group, which were forced to withdraw from southern urban centres.

The separatist STC wants the south to secede from the rest of the country, even while it is allied with the central government in a fight against their common foe, the Huthis, in the civil war.

The government and rebels have been locked in a five-year-old war that has killed tens of thousands -- triggering what the UN terms the world's worst humanitarian crisis.