The U.N. humanitarian aid agency said it's agreed with the rebel-run government in the capital of war-torn Yemen on a "medical air bridge" to evacuate civilians for medical treatment. The airlift would include those who suffer from chronic and critical health issues such as cancer or kidney trouble.

The Office for the Coordination of Humanitarian Affairs said late Sunday its Yemen coordinator, Lise Grande, signed a deal with Sanaa authorities to allow for "medical transfer of critically ill patients, by chartered air flight, to a medical facility that is equipped to manage such cases," according to the Associated Press. The World Health Organization's Yemen representative, Dr. Nevio Zagaria, said 12 "conditions" had been agreed on. WHO is setting up procedures for the air bridge, which would initially operate for a six-month "trial period." Some 21 million people, or three-in-four Yemenis, require some form of humanitarian assistance in the conflict-ravaged country. Yemen has been wracked by conflict since 2014, when Shiite Houthi rebels overran much of the country.

Saudi Crown Prince Mohammed bin Salman, the former defense minister, and Saudia Arabia's allies launched Operation Decisive Storm in March 2015. Riyadh has accused the rebel group of serving as a proxy force for Iran, Saudi Arabia's arch foe in the region.

Saudi Arabia and the United Arab Emirates may have been responsible for war crimes in Yemen, U.N. investigators said in a report revealed last month, highlighting deadly airstrikes, rampant sexual violence and the recruitment of young children as soldiers during three years of escalating conflict.