Malala celebrates her graduation with her first tweet

Malala Yousafzai, a Pakistani women's rights advocate and Nobel laureate, celebrated her last day of school on Friday in her first tweet on Twitter.

Yousafzai had been attending a school in the city of Birmingham where she was treated after a Taliban gunman shot her in the head for advocating education for girls in her native Swat valley in the Khyber Pakhtunkhwa Province of Pakistan.

She has since become a global icon for girls' education, winning the Nobel Peace Prize in 2014.

On Friday, Yousafzai completed her schooling in Britain, calling the achievement "bittersweet".

"Today is my last day of school and my first day on @Twitter," she wrote on her newly opened account, which gained more than 134,000 followers in three hours.

"Graduating from secondary school (high school) is bittersweet for me," she tweeted, adding: "I know that millions of girls around the world are out of school and may never get the opportunity to complete their education".

Excited about future

But she said she was "excited" about her future and promised to continue "fighting for girls".

She said on her new Twitter account that she would travel next week to the Middle East, Africa and Latin America to meet with girls.

Yousafzai has excelled at school and is awaiting the results of her A-level exams next month. She has been offered a place to study at Oxford University.

She has chosen to study Philosophy, Politics and Economics, a prestigious course that has produced many British politicians and world leaders including late Pakistani prime minister Benazir Bhutto.