Pope Benedict has come down hard on the EU for excluding any reference to God and the Christian heritage of Europe in a declaration to mark the 50th anniversary of its founding treaty on Sunday.

The "Berlin Declaration" was issued by German Chancellor Angela Merkel, current holder of the rotating EU presidency, to mark 50 years since the founding of the union in Rome in 1957.

The declaration highlights European values such as democracy and outlines a vision for the future which includes fighting climate change. It contains, however, no reference to God or to Europe's Christian roots.

In a hard-hitting speech to European bishops, the Pope accused Europe of abandoning God and the Christian faith - the dominant faith across the continent.

"If on the 50th anniversary of the Treaty of Rome the governments of the union want to get closer to their citizens, how can they exclude an element as essential to the identity of Europe as Christianity, in which the vast majority of its people continue to identify," he said in a Reuters report.

"Does not this unique form of apostasy of itself, even before God, lead it (Europe) to doubt its very identity?"

The Pope has, likewise, advocated strongly for a reference to God in the EU constitution, following in the footsteps of his predecessor John Paul.