Pope Francis is facing criticism in Brazil after it emerged he wrote a private letter to the country's embattled president Dilma Rousseff.

She's facing impeachment and a possible criminal trial amid allegations the government budget was manipulated.

Earlier this month Brazil's Senate voted to put the suspended president on trial for allegedly breaking fiscal rules in her managing of the federal budget.

The 59-21 vote is the final step before a trial and vote on whether to remove her from office, expected later this month.

The Senate voted in May to impeach and suspend Ms Rousseff from office for up to 180 days.

In the meantime, Michel Temer, who was Ms Rousseff's vice president-turned-nemesis, has taken over.

Ms Rousseff has repeatedly said she did nothing wrong.

She has now revealed Pope Francis wrote her a private letter: "Pope Francis wrote me a letter, but I will not divulge the content," she said.

"I can only say that it was not an official letter," she added.

Francis has since faced accusations of meddling in Brazilian politics with some saying the letter is an endorsement of Rousseff.

Most of Brazil's Catholic bishops have already publicly backed Ms Rousseff.