It has been one month since the hardline Islamist Taliban, which seized power in August, excluded girls from returning to secondary school while ordering boys back to class.
The Taliban have claimed they will allow girls to return once they have ensured security and stricter segregation under their interpretation of Islamic law, but many are skeptical.
“To the Taliban authorities…reverse the de facto ban on girls’ education and re-open girls’ secondary schools immediately,” Ms Yousafzai and a number of Afghan women’s rights activists said in an open letter.
Ms Yousafzai called on the leaders of Muslim nations to make it clear to the Taliban that “religion does not justify preventing girls from going to school”.
“Afghanistan is now the only country in the world that forbids girls’ education,” said the writers, who included the head of the Afghan human rights commission under the last US-backed government Shaharzad Akbar.
The authors called on G20 world leaders to provide urgent funding for an education plan for Afghan children.
A petition alongside the letter had on Monday received more than 640,000 signatures.
Education activist Malala was shot by militants from the Tehreek-e-Taliban Pakistan, an offshoot of the Afghan Taliban, in her home town in the Swat Valley while on a school bus in 2012.
Now 24-years-old, she advocates for girls’ education, with her non-profit Malala Fund having invested $2 million in Afghanistan.