Twenty-one separatist fighters and six members of Al-Qaeda's branch were killed on Tuesday, government and security sources said, as an attack by the punctured months of relative peace in the war-torn country.
Al-Qaeda in the Arabian Peninsula (AQAP) attacked positions held by the -trained Security Belt group in Abyan governorate in Yemen's south, the sources told AFP.
About three hours of fighting "left 21 dead among the (Security Belt), including an officer, and six among the Al-Qaeda combatants", a government official said on condition of anonymity. Two security sources confirmed the death toll.
Yemen has been gripped by conflict since Iran-backed Houthi rebels took control of the capital Sanaa in 2014, triggering a Saudi-led military intervention in support of the beleaguered government the following year.
AQAP and militants loyal to the have thrived in the chaos.
Tuesday's fighting comes as the Houthis and forces supporting the ousted government observe a shaky in the years-long civil war.
Riven by divisions, the groups opposing the Houthis, who originate from the north, include southern separatists who support the re-establishment of South Yemen.
The country was divided into North and South Yemen until reunification in 1990.
Underlining Yemen's parlous security, on Saturday AQAP released a video showing a worker who was abducted more than six months ago, the SITE Intelligence Group reported.
Five UN staff members were kidnapped in Abyan in February while returning to the port city of Aden after a field mission, UN spokesperson Eri Kaneko told AFP at the time.
In Saturday's video message, apparently recorded on August 9, Akam Sofyol Anam urges "the UN, the international community, the humanitarian organisations, to please come forward... and meet the demands of my captors", without outlining the demands.
Yemen's UN-brokered ceasefire has drastically reduced fighting since the truce began in April, but outbreaks of violence continue.
Last week, 10 Yemeni soldiers were killed in a Houthi attack near Taez, the country's third biggest city which has been blockaded by the rebels since 2015.
The assault, which also left several soldiers wounded, was aimed at cutting off a key route to the southwestern city of about two million, the government said.
On Thursday, the held a military parade in the Red Sea port city of Hodeida, drawing a rebuke from the UN.