Pope Leo blasted leaders who spend billions on wars and said the world was "being ravaged by a handful of tyrants", in unusually forceful remarks in Cameroon on Thursday after US President Donald Trump attacked him again on social media.

Leo, the first US pope, also decried leaders who used religious language to justify wars and urged a "decisive change of course" in a meeting in the biggest city in Cameroon's anglophone regions, where a simmering conflict going back nearly a decade has left thousands dead.

"The masters of war pretend not to know that it takes only a moment to destroy, yet often a lifetime is not enough to rebuild," the pontiff said.

"They turn a blind eye to the fact that billions of dollars are spent on killing and devastation, yet the resources needed for healing, education and restoration are nowhere to be found."

'A WORLD TURNED UPSIDE DOWN'

Trump's attacks on Leo, first launched on the eve of the pope's ambitious four-country tour of Africa and repeated late Tuesday, have caused dismay in Africa, where more than a fifth of the world's Catholics live.

Leo, who kept a relatively low profile for most of his first year as leader of the 1.4-billion-member Church, has emerged as an outspoken critic of the war that began with US-Israeli strikes on Iran.

On Thursday, the pontiff sharply criticised leaders who invoked religious themes to justify wars.

"Woe to those who manipulate religion and the very name of God for their own military, economic and political gain, dragging that which is sacred into darkness and filth," he said.

"It is a world turned upside down, an exploitation of God’s creation that must be denounced and rejected by every honest conscience."

The pope made similar remarks last month, saying God rejected prayers from leaders with "hands full of blood", in comments widely interpreted as aimed at US Defense Secretary Pete Hegseth, who has invoked Christian language to justify the Iran war.

Trump began his criticism of Leo on Sunday, when he called the pope "WEAK on Crime, and terrible for Foreign Policy" in a post on Truth Social.

The US president attacked him again on social media late on Tuesday, and on Wednesday Trump posted an image of Jesus embracing him, after an earlier image he posted that portrayed him as a Jesus-like figure prompted widespread criticism.

CLERGY CAUGHT UP IN CAMEROON CONFLICT

Leo told Reuters on Monday that he would not stop speaking out about the Iran war and has avoided responding to Trump directly since then.  

After arriving in the Cameroon capital Yaounde on Wednesday, he urged the government of the Central African nation - led by President Paul Biya, at 93 the world's oldest ruler - to root out corruption and resist "the whims of the rich and powerful".

Leo's trip on Thursday to the anglophone city of Bamenda has stirred faint hope that steps might be taken to resolve the conflict there, rooted in the country's complex colonial and post-colonial history.

Cameroon, a former German ​colony, was partitioned by Britain and France after World War One. The French part won independence in 1960 and was joined a year later by the smaller English-speaking British area to the west.

More than 6 500 people have been killed and more than half ‌a million displaced in fighting between government forces and anglophone separatist groups, ⁠according to the International Crisis Group. 

Priests are frequently kidnapped for ransom and some have been killed. A separatist alliance ⁠said it would observe a three-day ceasefire to allow civilians and visitors to move freely during the pope's visit.

Biya has not travelled to the anglophone regions since the fighting began.

Efforts to broker a ​peace deal have so far amounted to little, though on Thursday Leo said he was heartened that the crisis "has not degenerated into a religious war" and expressed hope that Christian and Muslim leaders could mediate an end to the fighting.