-Jesus may have heard words of wisdom from his mother Mary, but she did not help him save the world from damnation, the Vatican said on Tuesday.

In a new decree approved by Pope Leo, the Vatican's top doctrinal office instructed the world's 1.4 billion Catholics not to refer to Mary as the "co-redeemer" of the world.

Jesus alone saved the world, said the new instruction, settling an internal debate that had befuddled senior Church figures for decades, and even sparked rare open disagreement among recent popes.

"It would not be appropriate to use the title 'co-redemptrix'," said the text. "This title ... (can) create confusion and an imbalance in the harmony of the truths of the Christian faith."

Catholics believe Jesus redeemed humanity by his crucifixion and death. Church scholars have debated for centuries whether Mary, who Catholics and many Christians call the Mother of God, helped Jesus save the world.

The late Pope Francis fiercely opposed granting Mary the title of "co-redeemer", at one point calling the idea "foolishness".

"She never wanted to take anything for herself from her son," Francis, who died in April, said in 2019.

Francis' predecessor, Benedict XVI, also opposed the title. His predecessor, John Paul II, supported it, but stopped using the title publicly in the mid-1990s after the doctrinal office began expressing scepticism.

The new Vatican instruction highlighted Mary's role as an intermediary between God and humanity. By giving birth to Jesus, she "opened the gates of the Redemption that all humanity had awaited", it said.

According to the Bible, Mary's response to the angel who told her she would become pregnant was: "Let it be."