FIFA president Sepp Blatter on Tuesday appealed to his biggest critics to show unity and solidarity ahead of an election in which he faces an unprecedented challenge to his rule.

Blatter refused to appear with the three rivals challenging him for the leadership of football's governing body at UEFA's annual congress but made his plea in a speech at the start of the meeting.

Europe has led opposition to Blatter's bid for a fifth term. But without mentioning the FIFA election on May 29 and controversies that have engulfed his latest term, Blatter said all the heads of continental federations should rally round.

He called on the presidents of the European, Asian, North American and South American confederations, who were at the meeting, to show the "unity and this solidarity which exists as the foundations of football."

"Together with Europe, we need to build this unity on the inside and on the outside of your respective organisations," Blatter said.

The 54 European federations are expected to vote en masse against Blatter, but he said: "Europe is the root of the strength that helps all the other associations and five confederations. I would invite you to lead by example today and every other day."

He added: "Football can only be strong if the governing bodies and structures are strong and united. It is solidarity and unity. This is the message today, it is the message for tomorrow. It is the message for the future, for the good of the game, for the world and for UEFA."

Blatter's election opponents -- Prince Ali bin Al Hussein of Jordan, a FIFA vice president, Dutch federation chief Michael van Praag and former Portugal star Luis Figo -- are all to address UEFA in a special debate later Tuesday.

Blatter also renewed his condemnation of appeals for a boycott of the 2018 World Cup in Russia over the Ukraine conflict.

"Boycott has never given any results," he said.