Pope Francis has made an emotional anti-war address during a visit to a US military cemetery in Italy.
He said mass for several thousand people at the Sicily-Rome American Cemetery in Nettuno, south of Rome.
The burial ground is the final resting place for 7,860 American soldiers who died in the liberation of southern Italy and Rome in 1943 and 1944.
Francis walked slowly and alone amid the rows of low white headstones in the shape of crosses and Stars of David, gently resting a white rose on about a dozen and stopping to pray silently before saying the Mass.
'Please Lord, stop. No more wars. No more of these useless massacres,' he said, speaking in hushed tones in an improvised homily.
Appearing to refer to the possibility of nuclear war, he said that 'today that the world once more is at war and is preparing to go even more forcefully into war'.
It is not the first time the Pope has spoken of his fears of war and warned against escalating tensions. He said during the summer as relations between the US and North Korea deteriorated that a nuclear conflict would destroy a large part of humanity and that a third country should try to mediate in a situation that had become 'too hot'.
US President Donald Trump said North Korea 'will be met with fire and fury like the world has never seen' if it threatened the United States.
At the cemetery, Francis said: 'If today is a day of hope, it is also a day of tears.' He said humanity 'must not forget' the tears of mothers and wives who lost husbands and sons in past wars.
'Humanity has not learned the lesson and seems that it does not want to learn it,' he said.
On his way back to the Vatican, Francis stopped to pray at the Ardeatine Caves, where in March 1944 occupying Nazis killed 335 Italian men and boys as a reprisal for the killing of 33 German policemen by partisans.
They were all shot in the back of the neck. The Germans blew up the caves in a vain attempt to try to hide the massacre. Seventy-five of the victims were Jews.
He and Rome's chief rabbi, Riccardo Di Segni, each read a prayer. After walking past the tombs in the still dark caves, the pope wrote in the visitors' book: 'This is the fruit of war: hate, death, vendetta. Forgive us Lord'.
Additional reporting by Reuters.