Opening mass, the pontiff welcomed youths who had travelled to Rome.

"And how can we not express brotherly solidarity with all those young people suffering through the war and violence in Iraq, the Holy Land and other regions of the world?" he asked the crowd.

His Palm Sunday mass, to mark the entry of Jesus into Jerusalem and the beginning of the holy week of Easter, was dedicated to the Virgin Mary.

"In a certain way, Jerusalem can be considered the symbolic city of humanity, especially with this dramatic start to the third millennium that we are living through," he said.

The nearly 83-year-old pope, who suffers from Parkinson's disease and arthritis, looked well and spoke with a strong voice during the two-hour mass at St Peter's Square.

Sunday marks the 18th World Youth Day, which is celebrated by young Roman Catholics worldwide. A week-long festival marking the occasion is held every two years.

SPACE.WIRE