Pope Francis and UN Secretary General Antonio Guterres on Friday jointly appealed for religious tolerance and environmental protection.
The pair released a video message after meeting at the Vatican.
"It is good that this meeting of ours takes place in the days leading up to Christmas," the Argentinian Pope said in his native Spanish with Mr Guterres by his side.
"We cannot, we must not look the other way when believers of various faiths are persecuted in different parts of the world," the Pontiff added.
"It is a time of peace and goodwill and I am sad to see that Christian communities - including some of the oldest in the world - cannot safely celebrate Christmas," the UN Secretary General said.
"Tragically we see Jews being murdered in synagogues, their gravestones defaced with swastikas; Muslims gunned down in mosques, their religious sites vandalised; Christians killed at prayers, their churches torched."
Repeating the message he made in November during a trip to Japan for a world without nuclear weapons, Pope Francis said: "The use as well as possession of nuclear weapons... is also immoral."
The Pope also urged people to "take care of our land which, generation after generation, has been entrusted to our custody by God so that we may cultivate it and hand it over to our children".
Mr Guterres arrived in Rome five days after the UN's COP25 climate summit in Madrid and called on all countries around the globe to commit to carbon neutrality by 2050.
Pope Francis gave his guest a copy of the "human fraternity for world peace and living together" declaration which was signed by the Pope and the Grand Imam of Al Azhar, Dr Ahmed Al Tayeb, in the United Arab Emirates in February.
Considered a milestone in the dialogue between Christians and Muslims, the text calls for freedom of belief and expression, the protection of places of worship and advocates full citizenship for discriminated "minorities".
Mr Guterres said the text was "extremely important when we see such dramatic attacks on religious freedom and the lives of believers".
The Secretary General said the UN had launched an action plan to safeguard religious sites and a strategy to combat hate speech.