VATICAN CITY - Pope Benedict opened a synod of Roman Catholic bishops on Africa by denouncing the West's materialism and lack of moral values, which he said were contaminating the world's poorest continent like toxic waste.

In his homily, the Pope compared Africa, which he visited earlier this year, to a spiritual lung at risk of being attacked by what he called the viruses of materialism and religious fundamentalism.

There is absolutely no doubt that the so-called 'First' World has exported up to now and continues to export its spiritual toxic waste that contaminates the peoples of other continents, particularly those of Africa, he said.

In this sense colonialism, which is over at a political level, has never really entirely come to an end.

Lamenting the exploitation of Africa's vast resources, the pope also spoke out against religious fundamentalism, which he said was mixed with political and economic interests.

Groups who follow various religious creeds are spreading throughout the continent of Africa ...teaching and practicing not love and respect for freedom, but intolerance and violence.

In the 20th century, Africa's Catholic population shot up from about 2 million in 1900 to about 140 million in 2000, making the continent ever more important to the Vatican as the number of practicing Catholics in the developed world declines.

In his Angelus blessing, the Pope called for political dialogue in Guinea, where at least 157 people were killed in a bloody crackdown on street protesters on Monday.