The Vatican's foreign minister traveled to Yugoslavia to deliver the pope's appeal. John Paul also wrote Yugoslav President Slobodan Milosevic, President Clinton and NATO Secretary-General Javier Solana.
At the Vatican, the pope bathed the feet of 12 priests in a Maundy Thursday ceremony evoking Jesus' Last Supper with his apostles. The act recalls "in a profound sense the sacrifice of Christ," John Paul said in his homily.
The rite marks Jesus' washing of the apostles' feet the day before his crucifixion on Good Friday, and is maintained by the church as a symbol of humility.
John Paul poured water from a beaker on the feet of the clergymen as they sat in a row on a platform in St. Peter's Basilica.
The ceremony initially had been scheduled to take place in St. John Lateran Basilica. Vatican Radio said the venue was changed because of renovation work underway at St. John Lateran.
On Friday, John Paul will carry a cross in a traditional procession around the Coliseum, symbolically tracing Jesus' path to his crucifixion.
Th pontiff's Holy Week services culminate in an Easter Sunday Mass at St. Peter's Basilica.