Malala Yousufzai was shot in the head and neck when gunmen fired on her school bus in the Swat valley, northwest of the capital, Islamabad. Two other girls were also wounded, police said.
Taliban spokesman Ehsanullah Ehsan said his group was behind the shooting.
"She was pro-West, she was speaking against Taliban and she was calling President Obama her idol," Ehsan said by telephone from an undisclosed location.
"She was young but she was promoting Western culture in Pashtun areas," he said, referring the main ethnic group in northwest Pakistan and southern and eastern Afghanistan. Most members of the Taliban come from conservative Pashtun tribes.