Muslims are conquering Europe because Christians have become too selfish and pagan to defend the spiritual heritage of the continent, a Vatican cardinal said this week.

Miloslav Vlk, who has served as archbishop of Prague since 1991 and was considered as a successor to John Paul II, launched an outspoken attack on Christians living in Europe and accused them of allowing Muslims to "Islamise" the continent.

He warned that Europe would "fall" to Islam if people continued to deny their Christian roots.

In an interview published on his website, Vlk blamed immigration and high birth rates among Muslims for filling "the vacant space created as Europeans systematically empty the Christian content of their lives".

The 77-year-old said: "Europe has denied its Christian roots from which it has risen and which could give it the strength to fend off the danger that it will be conquered by Muslims – which is actually happening gradually. If Europe doesn't change its relation to its own roots, it will be Islamised.

"At the end of the Middle Ages and in the early modern age, Islam failed to conquer Europe with arms. The Christians beat them then. Today, when the fighting is done with spiritual weapons which Europe lacks while Muslims are perfectly armed, the fall of Europe is looming."

It was Muslims and not Christians, said Vlk, who were shaping the spiritual outlook of Europe. "The Muslims definitely have many reasons to be heading here. They also have a religious one – to bring the spiritual values of faith in God to the pagan environment of Europe, to its atheistic style of life."

In a separate interview, a second cardinal criticised Islam for repressing religious freedom.

Cardinal Jean-Louis Tauran, who served as the Vatican's foreign minister from 1990 to 2003 and was appointed president of the Pontifical Council for Interreligious Dialogue in 2007, urged countries to protect the right of religious freedom in their laws.

He told the Italian newspaper L'Osservatore Romano that such protection was assured in various Muslim countries with the exception of Saudi Arabia, where nearly 2 million Christians were deprived of public prayer gatherings. "They feel tolerated rather than a partner in public dialogue. And this does not do anyone any good."

He also commented on the Swiss referendum to ban the construction of new minarets, and seemed to approve of the outcome. "Naturally it is necessary to harmonize construction with the atmosphere in which it comes to be a part, with the city landscape, the cultural context, and the complex of the laws and norms that regulate the life of the society."