Washington: The world's top political and religious leaders have expressed shock and regret at Pope Benedict XVI's resignation, but declared respect for his tenure and leadership of 1.1 billion Catholics.
Plaudits and warm messages of support swiftly followed an announcement on Monday that the 85-year-old pontiff would step down this month due to old age, as victims of the church's child sex abuse scandal tempered the mood with avowed criticism.
"He is and remains one of the most significant religious thinkers of our time," Chancellor Angela Merkel, a pastor's daughter, said in a glowing tribute from the pope's native Germany.
In Washington, President Barack Obama offered "appreciation and prayers" on behalf of all Americans, saying he and his wife Michelle had warm memories from a 2009 meeting.
British Prime Minister David Cameron said Benedict would be "missed as a spiritual leader to millions" who had "worked tirelessly to strengthen Britain's relations with the Holy See".
And one of the most glowing tributes came from Brazil's Catholic bishops, who hailed the outgoing pontiff's "humility and greatness".
Closer to the Vatican, Italian President Giorgio Napolitano saluted the pontiff's "courage" over the decision to quit, making him the first pope in more than 700 years to step down, and after less than eight years in post.
Australian Prime Minister Julia Gillard focused on the difficulties of the pope's decision, and she praised him for nevertheless taking such a step.
"On his election, Joseph Ratzinger said he wished to be 'a simple humble worker in the vineyard of the Lord' and in his resignation that humility has been amply demonstrated," Ms Gillard said.
Australian Opposition Leader Tony Abbott said he would not be running for Pope as he had contemplated doing many years ago, but said Pope Benedict's resignation was ''not surprising''.
''Being the spiritual leader and chief administrator of more than one billion Catholics is an extraordinarily onerous job. Probably as tough as any job in the world and it's not surprising that at the age of 85 the Pope would decide after no doubt much contemplation that he doesn't have the necessary physical and mental stamina,'' Mr Abbott said.
Former National leader Tim Fischer, Australia's Ambassador to the Holy See between 2008 and 2012 said: ''This resignation is absolutely in accordance with canon law, it is courageous, it is the correct decision. I congratulate Pope Benedict the sixteenth.''
Joseph Ratzinger was the pope's name before he was made pontiff.
Bishop Marcelo Sanchez Sorondo, chancellor of the Vatican's Pontifical Academy of Sciences, said the pope's announcement caused "dismay and great sadness (in the Holy See) because he is a great pope".
From other world religions, Israel's Ashkenazi Chief Rabbi Yona Metzger told AFP that Benedict had improved ties between Judaism and Christianity that helped reduce anti-Semitism around the world.
Benedict's papacy "elevated Catholic-Jewish relations onto an unprecedented level," World Jewish Congress president Ronald Lauder said in a statement.
"No pope before him visited as many synagogues."
Justin Welby, head of the 85-million-strong worldwide Anglican communion as the new archbishop of Canterbury, said Benedict held his office with "great dignity, insight and courage".
The secretary general of the Mexican Episcopal Conference, Bishop Eugenio Lira Rugarcia, remarked that the Pope appeared diminished physically when he visited Mexico in March, but praised his leadership.
"Benedict XVI has been a completely open and transparent man, and this was a very honest decision," Lira Rugarcia told a news conference.
"The papacy of Benedict XVI has been very effective. His hand has not trembled in order to act firmly. He has taken very clear decisions."
But such remarks were met with scorn by groups representing victims of child abuse in Catholic-run institutions. They welcomed the resignation.
"This Pope had a great opportunity to finally address the decades of abuse in the church, but at the end of the day he did nothing but promise everything and in the end, he ultimately delivered nothing," said John Kelly, of the Irish Survivors of Child Abuse support group.
In Australia, the Survivors Network of those Abused by Priests issued a statement saying the pontiff had done little to stop "the reign of terror of child rapist priests", according to AAP.
And the US branch of SNAP said the Pope "still has two weeks" to take action against child sex abuse by church staff.
"Before he steps down, we hope he will show true leadership and compassion and take tangible action to safeguard vulnerable children," the group said.