Caroline Kennedy, the Roman Catholic daughter of the assassinated President, has been rejected by the Vatican as the next US ambassador to the Holy See because of her liberal views on abortion, stem-cell research and same-sex marriage, according to Vatican insiders.

Andrea Tornielli, the biographer of Pope Benedict XVI, said that at least two other potential ambassadors put forward by President Obama have also been blocked because they did not share the Vatican’s views on “pro-life” issues. A Vatican spokesman said that no candidates had been formally submitted “and therefore it is not true that they have been rejected”.

Vatican sources said that there had been “informal soundings” over a replacement for Mary Ann Glendon, the outgoing US ambassador to the Holy See, who is a Harvard law professor, president of the Pontifical Academy of Social Sciences and close to the Pope.

The Vatican hopes that the issue can be resolved before Mr Obama meets the Pope in the margins of the G8 summit to be held on the island of Sardinia in early July.

Raymond Flynn, a former US ambassador to the Vatican, told the Boston Herald that the views held by Ms Kennedy, 53, were “problematic”. “It’s imperative, it’s essential that the person who represents us to the Holy See be a person who has pro-life values,” he said.

Mr Obama was said to have wanted to reward Ms Kennedy for supporting his election. The other rejected nominees reportedly included Douglas Kmiec, professor of constitutional law at Pepperdine University and a former legal adviser to Presidents Reagan and George Bush Sr, who urged American Catholics to vote for Mr Obama.

Father John Jenkins, president of Notre Dame University in Indiana, a leading Catholic institution, has come under fire from some American Catholics for inviting Mr Obama to speak and offering him an honorary degree. Cardinal Francis George, Archbishop of Chicago and head of the US Conference of Catholic bishops, said: “Notre Dame didn’t understand what it means to be Catholic when they issued this invitation”.

Massimo Franco, author of Parallel Empires, a study of Vatican-US relations, said that the Vatican feared it would be sent an “American Zapatero”, a reference to José Luis Rodriguez Zapatero, the Spanish Prime Minister, attacked by the Church for having legalised same-sex marriage, introduced fast-track divorce and pulled religious instruction from the school curriculum.

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