Pope Francis has once again rejected claims that his concern for the poor and criticisms of capitalism make him a communist, by declaring that he is merely following the Gospel.

In one his longest speeches as Pope, the Holy See outlined his views on a wide range of issues– from poverty and the injustices of unemployment to the need to protect the environment.

"Today I want to unite my voice with yours and accompany you in your fight," he said to participants at the World Meeting of Popular Movements, which is holding a three-day conference in Rome involving groups including trade unions, peasant farmers, and domestic workers.

Among those in the audience were Argentine "cartoneros," who live off the sale of recyclable goods they salvage from rubbish. As archbishop of Buenos Aires, then-Cardinal Jorge Mario Bergoglio was particularly close to the cartoneros; as pope he has maintained his support for their plight. Anticipating how his letter would be received by his critics, Francis declared that “land, housing and work are increasingly unavailable to the majority’ of the world’s population,” but said “If I talk about this, some will think that the Pope is communist.”

"They don't understand that love for the poor is at the centre of the Gospel," he said. "Demanding this isn't unusual, it's the social doctrine of the church."

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His speech also further highlighted his concerns for the environment, as well as the rights of farmers to have land, and for young people to be employed – issues he said would be dealt with in his upcoming encyclical on ecology and the environment.

The address comes after right-wing US commentators said the Pope is a Marxist because he criticised capitalist excess and demanded that governments should redistribute social benefits to the needy.

Earlier this week, the Pope made headlines by declaring that scientific theories were compatible with the Christian belief of the existence of a creator, and said the theories of evolution and the Bing Bang are real.

Experts said the speech put an end to the “pseudo theories” of creationism and intelligent design that some argue were encouraged by his predecessor Benedict XVI.