Around 2.4 million girls are currently excluded from secondary schooling in Afghanistan as a result of Taliban government policy, according to an estimate published by the UN's Paris-based cultural organization on Tuesday.
"Women have been erased from public life, and as a new generation of girls grows without an education, their future becomes increasingly dark," it said.
That figure could rise to almost 4 million by 2030, UNESCO predicted.
The estimate is based on the number of girls who already enrolled in secondary school and had to leave after the Taliban took power, as well as girls currently completing primary school.
Afghanistan is the only country in the world to ban girls and women from receiving education beyond primary school. Two decades of progress were being undone as a result, UNESCO said.
After taking power in 2021, the Taliban drastically restricted women's rights. They are not allowed to attend secondary schools or universities. They are also largely being pushed out of the workforce.
UNESCO sees these restrictions as a serious human rights violations and forecasts that the exclusion of girls from education will worsen poverty in the country and leave potential untapped.
"At a time when nearly half of Afghans live below the poverty line, denying girls and women access to education and restricting their employment further undermines their ability to support their families and contribute to the country's economic future," it said.
The UN body believes that girls run the risk of marrying at a younger age and says the ban on continuing their education harms their well-being. UNESCO estimates that the country could lose around $9.6 billion in income by 2066, as numerous highly educated women are likely to have left the workforce by then.
UNESCO is working in Afghanistan to provide alternative learning opportunities. More than 69,000 people have participated in these programs since 2021, 70% of them girls and women.