Three Burundi schoolgirls arrested for allegedly scribbling on President Pierre Nkurunziza's photo have been released.

The girls were charged with "insulting the head of state" last Monday and could face up to five years in prison.

Their lawyer Nyanzira Prosper told the BBC the girls have been freed on bail until they appear in court.

Mr Prosper said their charges still stand and prosecutors will continue to investigate them.

"We appreciate the work of the court which looks to have acted with independence," he said of their release on Wednesday.

Addressing the allegations against them, Mr Prosper said there is "not any evidence of guilt" apart from the books being under their names.

He said he expects the girls, aged 15, 16 and 17, to go back to school in order to sit upcoming exams.

President Pierre Nkurunziza has been in power since 2005

Their detention has provoked international condemnation of the Burundian government, whose track record for human rights has come under scrutiny.

They were arrested two weeks ago after the president's image was defaced in textbooks. Four other students, arrested with them in Burundi's northeast Kirundo province, were later released.

Since their arrest, a campaign to "#FreeOurGirls" has swept social media, with users sharing doctored images of Nkurunziza in solidarity with the girls.

Hey @pnkurunziza, looking good.

SCRIBBLING IS NOT A CRIME - FREE THOSE GIRLS #Burundi #FreeOurGirls pic.twitter.com/Z8SD0vfLuJ

— Lomé Raumay (@kiwidrank) March 22, 2019

This @pnkurunziza's "presidential" advisor challenged ppl in the free world to doodle on pictures of their leaders. What followed was a worldwide mvt to doodle on Nkurunziza's pictures in solidarity w/ jailed schoolgirls in #Burundi.

Poor guy thinks repressive gvts are the norm https://t.co/gKYe7S7LQ7

— Thierry Uwamahoro (@ThierryU) March 23, 2019

The father of one of the detained girls told campaign group Human Rights Watch that they were too scared to eat.

HRW has urged the government to release the schoolgirls and concentrate on curbing abuses by the security forces.

"Authorities should focus on holding perpetrators of serious rights violations to account instead of jailing schoolchildren for doodles," the group's Central Africa director, Lewis Mudge, said.

In a similar case in 2016, several schoolchildren were imprisoned and hundreds expelled for scribbling on images of the president's face.

Burundi's ruling party has repeatedly denied allegations of human rights abuses.