NAIROBI (AFP) - Eleven high school students in a city in central Burundi were detained and charged Friday (June 3) with defacing a photo of President Pierre Nkurunziza, a police official said, as three people were shot and injured in a protest at the arrests.

"The prosecutor in Muramvya has just decided to detain 11... for insulting the head of state," the police official said, speaking on condition of anonymity.

"The children, six girls and five boys aged over 14, were placed in custody in Muramvya central prison in mid-afternoon."

The information was confirmed by several witnesses, including a parent who saw his daughter being taken off to the prison, and a lawyer who helped the students.

Insulting the president carries a potential jail term of five to 10 years, according to the country's penal code.

An impoverished country in central Africa struggling with a legacy of ethnic conflict, Burundi plunged into crisis in April 2015 when Nkurunziza announced he was running for a third term, a vote he won last July amid opposition boycotts.

Violence has left more than 500 people dead and forced more than 270,000 Burundians to flee the country, according to the UN.

The 11 students were rounded up on Friday morning by members of the national security service, the police said.

About a dozen others, aged under 14 - the age of criminal responsibility in Burundi - were released.

Hundreds of students at Muramvya municipal high school immediately rallied to demand the release of the 11, witnesses said.

"Policemen in the Burundi secret service opened fire to disperse the protest," said one source.

Two demonstrators were injured, along with a passing motorcyclist, the witnesses said.

In a separate incident last month, more than 300 students aged 14 to 16 were sent home from their school in the town of Ruziba after staff found a picture of the president had also been defaced in textbooks.

In some pictures the eyes had been gouged out, while insults against the president were scrawled over others.

Ruziba, a town in the county of Kanyosha just south of Bujumbura, is a stronghold of principal opposition leader Agathon Rwasa.