New York - UN Secretary-General Antonio Guterres is warning Burundi's President Pierre Nkurunziza against seeking a fourth term, saying such a move risks deepening the crisis in the African country.In a report obtained by AFP, the UN chief says he is "very concerned" by recent statements by Nkurunziza, in power since 2005, suggesting he could seek a fourth term in office, which would require changes to the constitution."An attempt by the president to seek a fourth term in office under the current circumstances would risk intensifying the crisis and undermining collective efforts to find a sustainable solution," wrote Guterres in the report sent to the Security Council on Thursday.Hundreds have died in violence in Burundi triggered by the president's decision in April 2015 to stand in elections for a third term in office, which he went on to win. Some 387 000 people have fled the country, and that figure is expected to surpass 500 000 in 2017, according to the UN refugee agency.Guterres expressed concern over the growing role of the ruling party's youth militia, known as the Imbonerakure, and said more than 200 cases of enforced disappearances since October were "of particular concern."The youth militia "is contributing to a sense of insecurity and a climate of fear" and is reportedly implicated in many cases of killings, arrests, disappearances, and some cases of sexual violence, he said.The report was sent to council members following the adoption of a resolution in July authorizing the deployment of up to 228 UN police to monitor security and human rights in Burundi.The government in Bujumbura has rejected the resolution and is still stonewalling the United Nations over the proposed police deployment, the report confirmed.Burundi's Ambassador Albert Shingiro described the report as "biased" and driven by UN envoy Jamal Benomar, whom he accused of "seeking revenge" after his government asked that he be replaced.The ambassador told AFP that it was "very surprising" that Guterres raised concerns about term limits for Nkurunziza "when many presidents in Africa and elsewhere are serving their fourth, fifth, sixth and seventh term without any concern being raised."Burundi this week again sent a letter to Guterres asking that a new envoy be named to replace Benomar.The Security Council postponed a meeting on Burundi scheduled for this week, but it is expected to discuss the crisis in March.