Conjoined Yemeni twins Mohamed and Ahmed took off on a UNICEF plane on Saturday to undergo a lifesaving separation surgery in Amman in Jordan.
The surgery is crucial to save the lives of the newborns.
Their father Yasser al-Bakheity said it could not be carried out in Yemen due to the limited resources of the country's ailing healthcare system.
The twins were born on December 17, conjoined by the rib cage and stomach.
Unicef's representative to Yemen is Philippe Duhamel.
"When the al-Sabeen hospital and the Ministry of Health informed UNICEF about the situation and asked for assistance, we immediately started mobilizing the UNICEF network to make sure that we would identify a hospital where the children could be properly treated."
Yemen has been gripped by war for 6 years between the Saudi-led alliance and Iran-aligned Houthis, creating what the U.N. calls the world's worst humanitarian crisis.