He had planned to visit the DR Congo cities of Kinshasa and Goma on 2 to 5 July before travelling to the South Sudanese capital, Juba, for a two-day trip.

However, the Vatican announced the postponement on Friday due to the 85-year-old pontiff's knee problem.

The pope told thousands of people in St Peter's Square that "with great regret, due to problems with my leg, I have had to postpone my visit to your countries".

He expressed hope that he will reschedule the visits “as soon as possible”.

The pope used a wheelchair for the first time at a public event in May due to reported pain in his right knee and has had to postpone a a scheduled trip to Lebanon this month.