In a video message, Akam Sofyol Anam, believed to be from Bangladesh, urges the global community "to please come forward...and meet the demands of my captors", without outlining the demands.
Al Qaeda's Yemen branch has released a video showing a United Nations worker who was abducted in the war-torn country more than six months ago, the SITE Intelligence Group has reported.
In Saturday's video message, apparently recorded on August 9, Akam Sofyol Anam, identified by SITE as Bangladeshi, urges "the UN, the international community, the humanitarian organisations, to please come forward... and meet the demands of my captors", without outlining the demands.
He said he was facing "serious health trouble", including heart problems, and needed "immediate medical support and hospitalisation", according to SITE, which monitors extremist activity.
Anam, who SITE identified as the "director of the United Nations Office of Security and Safety in Yemen", said he and four colleagues were kidnapped on February 11.
Five UN staff members were kidnapped in Yemen's southern province of Abyan in February while returning to the port city of Aden "after having completed a field mission," UN spokesperson Eri Kaneko said at the time.
"The United Nations is in close contact with the authorities to secure their release," its spokesperson had said after the workers' abduction in February.
Yemen has been gripped by conflict since the 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.
Hundreds of thousands have died, directly from fighting as well as indirectly, and millions have been displaced in what the UN has called the world's worst humanitarian crisis.
Aden became the base of Yemen's internationally recognised government after the Houthis ousted it from the capital Sanaa in 2014.
Al Qaeda in the Arabian Peninsula (AQAP) and fighters loyal to the Daesh terror group have thrived in the chaos.
Formed in a merger of Al Qaeda's Yemen and Saudi branches, AQAP has carried out attacks on both rebel and government targets in Yemen as well as foreigners.
It has also been accused of plotting attacks beyond the Middle East and its leaders have been targeted by a US drone war for more than two decades, although the number of strikes has dropped off in recent years.
Yemen's warring parties have been observing a ceasefire since April, bringing a drastic reduction in hostilities although small-scale fighting has continued.