Pope Benedict called in his Easter message on Sunday for an end to injustice worldwide and expressed joy at continuing conversions to Christianity hours after he baptised a prominent Italian Muslim convert.

The Pope celebrated an Easter Mass for tens of thousands of people in driving rain in St Peter's Square as Christians around the world commemorated Christ's resurrection.

The wind and rain that has whipped most of Europe did not spare Rome as the German pontiff, wearing white and gold vestments, said Mass while the crowd huddled under umbrellas.

The Mass came some 12 hours after an Easter vigil service on Saturday night where, in a surprise move, the Pope baptised Muslim-born convert Magdi Allam, 55, an outspoken journalist and fierce critic of Islamic extremism.

At the morning Mass, the Pope read a prayer saying that after Christ's resurrection some 2,000 years ago "thousands and thousands of people converted to the Christian faith" and he added: "This is a miracle that still renews itself today".

The Egyptian-born Mr Allam's conversion to Christianity - he took the name "Christian" for his baptism - was kept secret until the Vatican disclosed it in a statement less than an hour before the Saturday night service began.

Mr Allam, who is a strong supporter of Israel and whom an Israeli newspaper once called a "Muslim Zionist", has lived under police protection following threats against him, particularly after he criticised Iran's position on Israel.

Writing in yesterday's edition of the leading Corriere della Sera, the newspaper of which he is a deputy director, Mr Allam said he realised that he was in greater danger but he has no regrets.

Mr Allam wrote: "... the root of evil is innate in an Islam that is physiologically violent and historically conflictual".

His conversion, which he called "the happiest day of my life," came just two days after al Qaeda leader Osama bin Laden accused the Pope of being part of a "new crusade" against Islam.

The Vatican appeared to be at pains to head off criticism from the Islamic world about the conversion of Mr Allam, who defended the Pope in 2006 when the Pontiff made a speech that many Muslims perceived as depicting Islam as a violent faith.

"Conversion is a private matter, a personal thing and we hope that the baptism will not be interpreted negatively by Islam," Cardinal Giovanni Re told an Italian newspaper.

Still, Mr Allam's highly public baptism by the Pope shocked Italy's Muslim community, with some leaders openly questioning why the Vatican chose to shine such a big spotlight on it.

"What amazes me is the high profile the Vatican has given this conversion," Yaha Sergio Yahe Pallavicini, vice-president of the Italian Islamic Religious Community, said. "Why could he have not done this in his local parish?"

In his twice-yearly Urbi et Orbi (to the city and the world) message delivered after the Mass, the Pope decried "the many wounds that continue to disfigure humanity in our own day".