The Pope has replied to a vegan campaign offering him a million dollars to give up meat and animal products during Lent. 

In what could be interpreted as a polite no, Pope Francis replied in a letter to Genesis Butler, the 12-year-old vegan campaigner who issued the challenge, to say that he cared about the issues and that she was in his prayers. 

He declined to say one way or another whether he had actually accepted the challenge. 

'His Holiness Pope Francis has received your letter, and he has asked me to thank you,' said the response, which was signed by senior priest and Assessor for General Affairs, Paolo Borgia.

'He appreciates the concerns about care for the world, our common home, which prompted you to write to him.

'The Holy Father will remember you in his prayers, and he sends you his blessing.'

Pope Francis had been offered $1m to give to the charity of his choice if he pledged to adopt a plant-based diet during the season of Lent, which started yesterday on Ash Wednesday.

The generous offer was made by Matthew Glover, the co-founder of Veganuary, the month-long challenge to go vegan for the month of January. 

He said animal agriculture was 'rapidly driving' issues of climate change, world hunger and loss of biodiversity and that he wanted to challenge Pope Francis personally after the pontiff's own public statements of concern.

'We are launching this deliberately bold, audacious campaign to jolt our world leaders from their complacency,' said Glover.

'For too long they have failed to act on evidence of the damage caused to people and the planet by animal agriculture.

'Worse, many have defended and subsidised that very industry. But the evidence now is stark and compelling, and we cannot afford for them to remain silent any longer.

'We are thankful that Pope Francis has spoken out on these issues and that is why we are humbly asking him to try vegan for Lent, and set an example of how each of us can align our principles of caring and compassion with our actions.'

A petition asking Pope Francis to say yes to the challenge was signed by nearly 85,000 people.