Three Burundi schoolgirls who were detained for doodling on a picture of the President have been expelled from school following their release from jail, Human Rights Watch told CNN.

The girls, who are all minors, were detained for six days last month at Ngozi Central Prison and charged with "insulting the head of state," President Pierre Nkurunziza, according to the rights agency.

Their detention sparked worldwide anger with many taking to social media to post defaced pictures of Nkurunziza with the hashtag #FreeOurGirls.

A boy, who was not charged with any offenses but was arrested as part of the initial group of seven, and another girl were also expelled, HRW's Central Africa director Lewis Mudge told CNN.

“It's good news they were released, but the charges still haven';t been dropped, and they have now been expelled from school,” Mudge said.

“This is affecting their right to an education."

Mudge says authorities decided to expel them from the l';Ecofo Akamuri school in Kirundo province in Burundi';s north.

The Burundi government or the school authorities were not able to reach  for comment.

CNN, however, saw a letter dated March 20 from the school which stated that the students violated school regulations by "falsifying their schoolbooks."

“As stipulated by the school regulations in Article 31 paragraph 28, these five students are permanently expelled from school,” the letter read.

The letter, signed by the school';s director Isaie Nkinzingabo, also stated that the students will have to enroll at another school in the following academic year.

Mudge said the rights group doesn';t know why the boy was expelled from school as he was not among those initially charged.

“This demonstrates the way schools are being politicized in Burundi,” Mudge said.

“It also shows there are some individuals who are saying that this is such an intolerable act they feel the need to permanently expel these children.”

Previously, schoolchildren in Burundi were jailed and expelled for similar offenses.

In 2016, agents of the National Intelligence Service of Burundi arrested eight secondary school students for allegedly insulting Nkurunziza by writing phrases like "Get out" or "No to the 3rd term" on a picture of the President in a textbook, according to Human Rights Watch.

The same year, hundreds of children were expelled from several schools for scribbling on the President';s face in their books.

President Nkurunziza, who has been in office since 2005, was re-elected to a third term in 2015 despite massive protests and concerns over the legality of running beyond his second term.

But Burundi';s constitutional court ruled that he was eligible because he was picked by parliament, not elected by people, during his first term.

Scores died in the violence that marred the 2015 vote.

In early March, the United Nations High Commissioner for Human Rights Michelle Bachelet said the agency was forced to shut its local office of 23 years under concerted pressure from the Burundian government.