Nobel peace laureate Malala Yousafzai on Sunday called for global support to help release more than 200 Nigerian schoolgirls kidnapped by Boko Haram, as they marked 300 days as hostages.

"As we mark this tragic 300th day of captivity for hundreds of kidnapped Nigerian schoolgirls, I call on people everywhere to join me in demanding urgent action to free these heroic girls," she said.

Boko Haram fighters seized 276 teenagers from the Government Girls' Secondary School in the remote town of Chibok, in Borno state, northeast Nigeria, on April 14.

Fifty-seven managed to escape but 219 are still being held, despite military claims that they had been located but that a rescue operation was too fraught with danger to be conducted.

The girls' abduction and subsequent claims from Boko Haram leader Abubakar Shekau that they have been forcibly converted to Islam or married off sparked global outrage.

On Sunday, Malala said the government in Abuja and the international community "can and must do much more to resolve this crisis and change their weak response to date".

"If these girls were the children of politically or financially powerful parents, much more would be done to free them.

"But they come from an impoverished area of northeast Nigeria and, sadly, little has changed since they were kidnapped," Malala said in a statement.