With frailty and age comes a new phase of papacy - Pope

STORY: "I don't think I can continue doing trips with the same rhythm as before," he said in answers to reporters' questions aboard the plane returning from a week-long trip in Canada.

For the past few months the 85-year-old Francis has been using a wheelchair, a cane or a walker because of pain in the knee caused by fracture and inflamed ligament.

He walked with a cane to the rear cabin where reporters travel but sat in a wheelchair for the traditional, 45-minute news conference, the first time he has done so on his 37 international trips since his election in 2013.

"I think that at my age and with this limitation I have to preserve myself a bit in order to be able to serve the Church, or decide to step aside," he said.

The pace of the trip to Canada, which centered on his apologies for the Church's role in residential schools to assimilate indigenous children, was slower than in the past, with usually only two events a day and long patches of rest time.

Francis said he preferred not to have an operation on his knee because he did not want a repeat of long-term negative side effects from anesthesia he suffered after an intestinal operation a year ago.

"But I will try to continue to travel in order to be close to people because it is a way of serving," he said.

He indicated that he would first make trip to places he had already promised to go, such as South Sudan, Democratic Republic of Congo, Lebanon and perhaps Kazakhstan before deciding on future trips.

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