Al-Qaida is now operational in parts of war-torn Yemen, the UN warned on Tuesday.
A new UN human rights report claimed "other armed actors" -- including extremist groups like al-Qaida -- had taken advantage of the chaos gripping Yemen.
Al-Qaida in particular had a presence in Taiz city, southwestern Yemen, the UN added.
At least 5,144 civilians have been killed and more than 8,749 civilians injured in Yemen's conflict over three years, the report said.
Impoverished Yemen has remained in a state of civil war since 2014, when Houthi rebels overran much of the country, including the capital Sanaa.
The conflict escalated when Saudi Arabia and its Arab allies launched a massive air campaign in 2015 aimed at reversing Houthi military gains and shoring up Yemen's embattled government.
Tuesday's report said a humanitarian crisis gripping the country had 7.3 million people on the edge of famine, while 18.8 million in total needed humanitarian assistance.
A total of 2,043 people have been killed by a cholera epidemic since late April, the World Health Organization (WHO) also said on Tuesday.
The WHO said 602,526 suspected cases of cholera have been recorded in the country since April 27.
