A diplomatic solution must be found to the escalating tension between North Korea and the United States, Pope Francis has told journalists.

"The path is the path of negotiation, the path of a diplomatic solution," he said when asked about US President Donald Trump's decision to send Navy warships to the region in response to North Korea's continued missile tests and threats to launch nuclear strikes against South Korea, Japan and the United States.

"What do you say to these leaders who hold responsibility for the future of humanity," the Pope was asked, during a Q-and-A with journalists on the flight to Rome after a 27-hour trip to Cairo.