The 71-year-old pontiff said he was particularly concerned about the humanitarian situation in the southwestern Yemeni city of Taiz, "where the population suffers due to the lack of food, water and medical assistance".
He waved and smiled to the crowds after reaching the window unaided — the same spot where he announced on October 11 that he would have an operation to remove a small growth on his lung, in the first health scare of his papacy.
"I'm making a heartfelt appeal for the hostilities to stop, so that the people in Yemen and across the entire region can live in peace," he said in a very firm and clear voice.
The pope said he was also praying for those who had been killed and wounded in the "terrorist attack against Orthodox faithful" at the Hamoud church in Jordan on Friday.
"I'm close to that community and the entire country, which is known for the peaceful and respectful coexistence of different religions," the pontiff said.
Pope Leo urged everyone to accompany with prayers a meeting of religious leaders to promote peace that will take place in the Italian city of Assisi on Tuesday.
He had been due to attend that event, but cancelled his visit on the advice of doctors to aid his recovery, the Vatican said on Friday.
The pope had the lower lobe of his right lung removed in surgery on October 13 after being diagnosed with adenocarcinoma, the most common form of lung cancer.
Last week, doctors said he would not need any further therapy, indicating that his tumour had not spread.
