Vatican City: -Pope Francis' July 2-7 trip to the Democratic Republic of Congo and South Sudan has been indefinitely postponed because of the 85-year-old pontiff's knee ailment, the Vatican said on Friday.

A statement said the postponement was made 'with regret' at the requests of the pope's doctors, who have been treating him for a torn ligament in his knee. The condition has forced him to use a wheelchair for the last month or so.

The decision was taken "in order not to jeopardize the results of the therapy that he is undergoing for his knee," the statement by spokesman Matteo Bruni said.

Pope Francis was planning to spend July 2-5 in the Congolese cities of Kinshasa and Goma, and July 5-7 in the South Sudanese capital Juba.

The announcement was made just a few days after the Vatican had released the names of journalists whose requests to accompany the pope on the papal plane had been accepted and published and preparations in both countries were well underway.

The 85-year-old has been suffering from a painful inflamed ligament in his knee, limiting his ability to walk. He has been using a wheelchair during public appearances since last month.

He is still scheduled to visit Canada on July 24-29.