Pope Francis has again condemned Israeli air strikes in besieged Gaza, a day after an Israeli government minister publicly denounced the pontiff for suggesting the global community should study whether the Israel carnage there constitutes a genocide of the Palestinian people.

Francis opened his annual Christmas address to the Catholic cardinals who lead the Vatican's various departments with what appeared to be a reference to Israeli air strikes on Friday that killed at least 25 Palestinians in Gaza.

"Yesterday, children were bombed," said the pope on Saturday. "This is cruelty. This is not war. I wanted to say this because it touches the heart."

The pope, as leader of the 1.4-billion-member Roman Catholic Church, is usually careful about taking sides in conflicts, but he has recently been more outspoken about Israel's military attacks on Gaza against Palestinians.

In book excerpts published last month, the pontiff said some international experts said that "what is happening in Gaza has the characteristics of a genocide".

Israel accuses Pope of double standards

Israel has accused Pope Francis of "double standards" following his remarks.

"The Pope's remarks are particularly disappointing as they are disconnected from the true and factual context," the Israeli Foreign Ministry said.

"Enough with the double standards and the singling out of the Jewish state and its people."

Israel has killed over 45,000 Palestinians, mostly women and children, in its carnage in Gaza so far.

Tel Aviv has caused a massive shortage of basic necessities in its onslaught, including food, water, electricity and medicine, while displacing almost the entire population.

November 21, the International Criminal Court issued arrest warrants for Israeli Prime Minister Benjamin Netanyahu and former Defence Minister Yoav Gallant for war crimes and crimes against humanity in Gaza.

Israel also faces a genocide case at the International Court of Justice for its military campaign in the enclave.