VATICAN CITY, May 9 (Reuters) - Pope Leo XIV celebrated his first Mass on Friday in the Sistine Chapel where he was elected less than 24 hours earlier, warning of the dangers caused by a lack of faith and hoping the Catholic Church could be a beacon lighting the world's "dark nights".

Leo, the former Cardinal Robert Prevost and the first U.S. pope, looked calm as he delivered the Mass in the famous, frescoed chapel with the same cardinals who chose him to be the 267th pontiff and the successor to Pope Francis.

Dressed in relatively simple white and gold vestments, Leo, who was born in Chicago but spent two decades as a missionary in Peru, said a few words in English before continuing his homily in fluent Italian.

In the homily, Leo, 69, painted a picture of the Church he would like to see, saying he would seek to serve as the "faithful administrator" for the Church as a whole.

The new pope, who leads 1.4 billion Catholics around the world, acknowledged that the Christian faith is sometimes "considered absurd" and the preserve of "the weak and unintelligent".

"A lack of faith is often tragically accompanied by the loss of meaning in life, the neglect of mercy, appalling violations of human dignity, the crisis of the family and so many other wounds that afflict our society," he said.

Photo from Reuters