Madonna has called for more people to adopt children from Africa despite the controversy surrounding her own moves to take custody of a Malawian child.

The singer told US talk show host David Letterman she was "saving a life" by taking the one-year-old to the UK.

She admitted she had been warned it might be difficult but had not expected so much criticism.

The 48-year-old suggested laws needed to change because a million children in Malawi needed to be "rescued".

Some groups in Malawi have expressed concern that Madonna was able to bypass laws about foreigners adopting children.

She has also faced criticism this week from actress Angelina Jolie, who has adopted children from Cambodia and Ethiopia as well as having a daughter with actor Brad Pitt.

Jolie said in a magazine interview she would have steered clear of adopting from a country where there was no legal framework for adoption.

Madonna said she was warned by a social worker that adopting a child from Malawi could be difficult.

"She didn't say don't do it, but she just said expect challenges, and, boy, did we get them."

She added: "We were basically creating the laws as we went."

Madonna also has a nine-year-old daughter and six-year-old son.