It has emerged that US President-elect Barack Obama held his first telephone conversation with Pope Benedict XVI yesterday, the day a senior Vatican official made clear the Holy See would oppose any changes by Mr Obama in US policy on embryonic stem cell research.

The Vatican said the conversation on Tuesday formed part of the "normal exchanges" between a new American President and other world leaders. Father Federico Lombardi, the Pope's spokesman, said neither the Pope nor Mr Obama had made any reference to the stem cell issue during the call, in which Mr Obama had responded to the Pope's message congratulating him on his election win.

At a press conference on Tuesday the Vatican on infant mortality, Cardinal Javier Lozano Barragan of Mexico, the Pope's "health minister", strongly reiterated the Vatican's opposition to using embryos for research purposes when asked about signs that Mr Obama might reverse or relax the Bush administration's executive order banning the use of embryos and limiting federal spending for stem cell research. He said embryonic stem cell research "served no purpose".

Monsignor W. Francis Malooly, the Catholic bishop of Wilmington in Delaware, said he would not ban Joe Biden, the Vice President elect and a Roman Catholic, from taking Communion because of his stand on issues such as stem cell research and abortion. Mr Biden, a Senator from Delaware, lives in the Wilmington diocese.

The bishop was quoted as saying that "the Eucharist must not be politicised". He added that the job of a Catholic prelate was not to "alienate people" but rather to "change their hearts and minds". A number of Catholics in the senior ranks of the US Democratic Party take a liberal pro-choice stand on abortion, including Nancy Pelosi, the Speaker of the House, and John Kerry, the former Presidential candidate who has been tipped by some to become Secretary of State in the Obama administration.

Last month Bishop Malooly said Senator Biden had presented "a seriously erroneous picture of Catholic teaching on abortion" by saying on "Meet the Press" that the Church has "a nuanced view of the subject that leaves a great deal of room for uncertainty and debate."

The bishop said "This is simply incorrect. The teaching of the Church is clear and not open to debate. Abortion is a grave sin because it is the wrongful taking of an innocent human life. The Church received the tradition opposing abortion from Judaism. In the Greco-Roman world, early Christians were identifiable by their rejection of the common practices of abortion and infanticide."

He added: "The Didache, probably the earliest Christian writing apart from the New Testament, explicitly condemns abortion without exceptions. It tells us there is a "way of life" and a "way of death" and abortion is a part of the way of death. This has been the consistent teaching of the Church ever since."

This was also "the position of Protestant reformers without exception. It was the teaching of Pope John XXIII as well as Pope John Paul II. It is the teaching of Pope Benedict XVI and the bishops of the Church, including me as shepherd of this diocese."

He said he hoped Senator Biden "will carefully listen to the Church's 2000 years of testimony on abortion and that he will join in the defence and promotion of the sanctity of life." He intended "to build a supportive and trusting friendship" with Mr Biden and other public officials "to help them and all citizens understand how crucial the sanctity of human life is to a just society."