The Pope has issued a strong warning against those tempted by personal charisma to be authoritarian leaders in the Church, describing such leaders as "servants of the devil".

Addressing 30,000 Catholic faithful at a Catholic charismatic renewal conference at St Peter's, Rome, Pope Francis said he preferred to use the term "servant" than "leader".

He warned against the temptation for leaders to believe themselves essential to all tasks and described such leaders as "peacocks".

He warned: "The devil takes them to want to be the ones who command, those that are at the heart and so, step by step, slide into authoritarianism, personalism and leave no living communities renewed in the Spirit."

Such people would be drawn by this temptation into considering themselves irreplaceable, and would draw power and domination over others to themselves.

"We have this clear: the only irreplaceable in the Church is the Holy Spirit, and Jesus is the only Lord," he said.

Pope Francis was speaking to 30,000 faithful in St Peter's Square during the 38th National Convocation of Renewal in the Holy Spirit. During the meeting, the tenor Andrea Bocelli and other performers gave a powerful rendition of the spiritual hymn 'Amazing Grace'.

The meeting, with the theme, "Roads to unity and peace - pray for the martyrs of today and for spiritual ecumenism", was of leaders and followers of the Catholic charismatic renewal movement, of which Pope Francis is an enthusiastic advocate.

Cardinals present included Leonardo Sandri, Prefect of the Congregation for the Oriental Churches, Kurt Koch, President of the Pontifical Council for Promoting Christian Unity and Angelo Bagnasco, President of the Italian Bishops' Conference, along with the Eastern Orthodox Patriarchs, Catholic, Anglican and Lutheran bishops and Pentecostal pastors.

The Pope referred to the "current of grace" that runs through the Church and singled out for praise Veronica O'Brien, the Irish lay woman who was an influential figure in the 20th century Catholic charismatic movement. "Men and women who, having received the grace of baptism in the Spirit, as a result of this grace have created associations , covenant communities, training schools, schools of evangelisation, religious congregations, ecumenical community, communities to help the poor and needy," he said.

He said unity is not uniformity, and that unity exists in diversity. "The distinction is important because we are talking about the work of the Holy Spirit, not ours." There could be as many diverse expressions as the Holy Spirit wanted to provoke, he said.

"What is the common sign of those who are born again by this current of grace? Converted into new men and women, in the Baptism in the Spirit." He referred specifically to John 3, verses 7-8, when Jesus spoke to Nicodemus about rebirth in the Spirit.

"There is another point which is very important to clarify, in this current of grace: those who drive. There, dear brothers and sisters, it is tempting for leaders - and I repeat, I prefer the term servants, serving - the temptation is for the servants of the devil, to believe themselves essential, whatever the task."

He compared such abuse of leadership in the church to dictatorships.

He asked the crowd present: "Who is the only irreplaceable in the Church?" They responded en mass: "The Holy Spirit!" He repeated the chant: "And who is the one Lord?" They replied: "Jesus!"

The Pope also said charismatics have a "special grace" to pray and work for the unity of Christians. Catholics must be prepared to pray with Christians of other denominations, with Orthodox, with Lutherans.

"We have all received the same baptism, we are all going on the road of Jesus, we want Jesus... The work for Christian Unity begins with prayer. Pray together."

Christians should not distinguish between each other, just as their persecutors do not.

"We know that when those who hate Jesus Christ kill a Christian, before killing him, do not ask him: 'But you are a Lutheran, you are Orthodox, Evangelical you are, you're Baptist, you're Methodist?' You are a Christian! Cut your head off."

Those who hate Jesus Christ led by the evil one do not make mistakes, he said. "They kill with no questions asked."

He said the 23 Egyptian Copts who were slaughtered on the beach of Libya while saying the name of Jesus were true Christian martyrs, as were young martyrs of Uganda, who included Anglicans.

And he spoke of a longing to organise seminars about "life in the spirit" with other, non-Catholic charismatic churches, and for the benefit the poor and deprived living on the streets. "They too have the Spirit inside that pushes," he said.