Pope Francis' knee pain was so bad on the way to Bahrain on Thursday that he was unable to walk around the papal plane greeting accompanying reporters as he usually does.

The 85-year-old pope has walked with a cane since he tore a ligament in his knee early this year and he sometimes uses a wheelchair, but during flights he has always managed to walk around to exchange a few words with the Vatican press corps.

"Today I have a lot of pain and I am not up to moving around the plane so I'll sit down and you come to me," Francis told reporters during the flight to Bahrain for a four-day trip.

He said he had physical therapy on Wednesday and his knee always hurts the day after.

Despite the pain Francis appeared in good spirits as journalists greeted him individually at the front of the plane.

"It will be an interesting trip that will make us think," Francis said.

The Nov. 3-6 trip is aimed at improving ties with the Islamic world but the pope must also navigate a conflict in Bahrain over human rights that pits the Sunni Muslim monarchy against its Shi'ite Muslim opposition.

Francis will address the "Bahrain Forum for Dialogue: East and West for Human Coexistence," hold talks with King Hamad bin Isa al-Khalifa, and meet the Muslim Council of Elders at a mosque in the royal palace compound.

Bahrain has said the interfaith forum it is hosting during the pope's visit aims to "further cement the values of peace and tolerance," including dialog to promote coexistence.