The head of the Catholic Church, which has around 1.4 billion members worldwide, said he was thinking of the many innocent victims, including several children, as well as those who tried to help them, according to a statement from the Holy See released on Monday evening.
Leo said he was praying for a swift end to the hostilities.
The Vatican's statement also mentioned Lebanese priest Pierre al-Rai, who, according to reports from Lebanon, was killed in an Israeli military strike on the Christian village of Klajaa in the south of the country.
The mayor of the village, Hana Daher, told dpa on Monday that the priest was killed and five other people were wounded in a double Israeli strike on the Christian village.
Daher said the initial strike had hit a house.
"We rushed with the priest to help a man and woman inside the house," she said.
A second strike followed, which killed the priest and wounded five others, one of whom remains a serious condition, she said.
The Israeli military said its forces had targeted a Hezbollah cell.
Lebanon is a multi-confessional state. The population of is made up of several religious groups, including Sunni and Shia Muslims as well as Christians.
In December, Leo travelled to Lebanon on his first foreign trip as pope. He visited various Christian sites there. In the war-torn and crisis-ridden country, he repeatedly called for peace.
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