Chat show queen Oprah Winfrey, actress Meryl Streep and singer Elton John called on Monday for world leaders to put girls at the heart of anti-poverty efforts as a new index revealed Niger was the toughest country to be a girl.
In an open letter, published on the eve of International Women's Day, a host of prominent figures urged leaders to improve girls' and women's access to education, justice and technology and help them fight HIV and malnutrition.
They said it was "an outrage" that girls make up three-quarters of all new HIV infections among adolescents in Africa and that 40 percent of women on the continent suffer from anaemia which results in a fifth of maternal deaths.
"Nowhere on earth do women have as many opportunities as men," the letter added.
"While the debate around this truth rages everywhere, girls and women living in extreme poverty - those often hit hardest by the injustice of gender inequality - have been left out of the conversation. This must change. The fight for gender equity is global."
Other signatories included boxer Muhammad Ali, actors Robert Redford and Colin Farrell, actresses Charlize Theron and Patricia Arquette, Facebook CEO Sheryl Sandberg and U2 singer Bono, co-founder of anti-poverty charity ONE which published the letter.
One said being born a girl in a poor country amounted to a "double whammy".
"In too many countries being born poor and female means a life sentence of inequality, oppression and poverty - and in too many cases also a death sentence," it said in a report entitled Poverty is Sexist.
In Niger a woman has a one in 20 chance in her lifetime of dying while giving birth.
In an index compiled by ONE of the 20 hardest countries to be a girl, Niger is followed by Somalia, Mali, Central African Republic, Yemen, Democratic Republic of Congo, Afghanistan, Ivory Coast, Chad and Comoros.
Globally, half a billion women cannot read, 62 million girls are denied an education and 155 countries still have laws that discriminate against women.
But ONE said investments targeted towards girls and women paid dividends by lifting everyone out of poverty more quickly.
It said 2016 presented two big opportunities for leaders to turn into action the commitments they made on gender inequality when they adopted the new U.N. Sustainable Development Goals last year.
These are the Nutrition for Growth Summit hosted by Rio in August and the replenishment of the Global Fund to fight AIDS, TB and Malaria, which is aiming to raise $13 billion.
ONE policy director Eloise Todd said investing in nutrition and health was vital not just for women and girls but for the fight against extreme poverty.
"Until leaders tackle the injustices that pervade the lives of girls and women and invest in fighting poverty, half of the world's resources will remain untapped, and social and economic progress for everyone will be constrained," she added.