The top United Nations human rights official has called on authorities in Burundi to act, after reports of campaigns to 'impregnate or kill' opponents.

UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said there is an apparent "widespread pattern" of rallies in many places where young men repeatedly chant the call.

He said these men are from the Imbonerakure militia, the youth wing of the ruling political party, and that it is "particularly worrying" that, senior government officials are taking part in such rallies.

He said: "The grotesque rape chants by the young men [...] are deeply alarming - particularly because they confirm what we have been hearing from those who have fled Burundi about a campaign of fear and terror by this organized militia".

A statement from the Office of the High Commissioner says a "chilling video" circulating on social media shows a rally in which more than 100 Imbonerakure members are seen repeating dozens of times their call to "make opponents pregnant so that they can give birth to Imbonerakure".

In the same video, another group then repeats a chant "he or she should die".

The UN noted that the ruling CNDD-FDD party issued a statement on April 5th condemning the chanting.

But it also found recent reports indicate that similar, larger rallies have been organiaed across the country by officials from the government and the president's party.

Mr Zeid added: "Condemnation is meaningless if, instead of a putting a stop to such events, senior government officials continue to take part in such rallies.

"The government needs to stop pretending that the Imbonerakure are nothing but a community development group. Such blatant and brazen hate speech and incitement to violence must not be tolerated, nor encouraged."

Map of Burundi | Image: UN/Department of Field Support Geospatial Information Section

Civil unrest

The UN rights chief also voiced concern over continuing reports of serious human rights violations in the African country, including "systematic use" of torture by security forces, increasing cases of enforced disappearance, nightly raids by the Imbonerakure militia into homes of people who refuse to join the ruling party, and people targeted because of their ethnicity.

The UN estimates more than 400,000 people have fled the African nation over the last two years fearing for their safety.

The United Nations has been present in Burundi under mandate by the Security Council since 2004.

Civil unrest flared in in April 2015, after the ruling party elected President Pierre Nkurunziza as its candidate.

While elections were considered relatively peaceful, the UN reported the overall environment was "not conducive" to an inclusive, free and credible process.

Since then, hundreds of people have reportedly been killed. Some 220,000 people have sought refuge in neighbouring countries and thousands more displaced.

In responce to the violence, a special adviser for conflict prevention was appointed by the UN in 2015.

Last July, the UN Security Council authorised the deployment of a police contingent in to monitor human rights and the security situation.