Pope Benedict XVI said that unifying all Christians and healing the 1,000-year rift between Catholics and the Orthodox is particularly urgent nowadays.
In the message to a Catholic-Orthodox symposium on Sunday, the pope called for intensified prayers and dialogue to help heal the rift, which he has said would be a fundamental priority of his pontificate.
"The search for the full, visible union among all the disciples of Christ is seen as particularly urgent in our times, and for this one feels the need for a more profound spirituality and an increase in reciprocal love," the pope said in his message.
The Catholic and Orthodox churches split in 1054 over several questions, including the issue of the primacy of the pope. Relations now between the two sides have been made tense by Orthodox charges of aggressive Catholic missionary work in Eastern Europe and by property disputes.
Theological dialogue was interrupted four years ago, but in June both sides announced that talks would resume, the AP reminds.
In his message, Benedict said it was unfortunate that the lack of full unity meant that Orthodox and Catholic priests could not jointly celebrate Mass.
"Realizing full communion of Christians must be an objective for all those who profess faith in" one church, he said.
The symposium, held in the hilltown of Assisi, was organized by the Pontifical Antonianum University and the theology department of the University of Thessaloniki, in the city of the same name, in Greece.