NAIROBI (Reuters) - Four Burundian journalists arrested this week were charged on Saturday with undermining state security, an editor at their newspaper tweeted, as Burundi’s government clamps down on journalists and human rights groups ahead of elections in 2020.

The journalists from domestic news website Iwacu and their driver had traveled to report on violence in the northwestern province of Bubanza when they were arrested on Tuesday.

Security forces had said they killed 14 people in the province who had crossed the border from the neighboring Democratic Republic of Congo.

The media outlet had also received reports of rebel attacks and abductions of civilians. Editors decided to send radio journalist Christine Kamikazi, political reporter Agnès Ndirubusa, English-language journalist Egide Harerimana, photographer Térence Mpozenzi and driver Adolphe Masabarakiza to check on the situation.

They were arrested while interviewing civilians, Iwacu said on its website.

Now the group has been formally charged with “complicity in undermining the internal security of state,” tweeted Pierre Emmanuel, an editor at the website.

Hundreds of Burundians have been killed in clashes with security forces since 2015, when President Pierre Nkurunziza ran for a third, disputed term in office. The opposition said his candidacy violated the terms of the peace deal that ended the east African nation’s civil war.

In the last few years, Nkurunziza has clamped down on civil rights by withdrawing from the International Criminal Court, expelling U.N. human rights investigators, shutting down rights groups and forcing journalists into exile. Schoolgirls who scribbled on his portrait were arrested.

Burundi is due to hold elections next year after Nkurunziza won a referendum last year that could allow him to stay in office until 2034.

“Charging journalists doing their jobs with state security crimes is an assault on all journalists in Burundi trying to uncover the truth about what is going on in Burundi. This is an attempt to intimidate and silence the few remaining independent journalists left in the country,” said Lewis Mudge, Central Africa Director at Human Rights Watch.

“The message is clear: in the run up to the electoral period, do your job and you will be punished.”

Last month the U.N. released a report saying police, security forces and the ruling party’s youth league, the Imbonerakure, carried out killings, disappearances, torture and gang rape of people perceived to be opposed to the president.