By Stephanie Nebehay

GENEVA (Reuters) - The United Nations High Commissioner for Human Rights said on Wednesday he feared increased violence and incitement in Burundi's crisis could turn ethnic in nature, but the government rebuffed his comments.

U.N. human rights chief Zeid Ra'ad Al Hussein also told a meeting in Geneva while giving a report on Burundi that he was concerned about suspensions and arrests of students for defacing portraits of President Pierre Nkurunziza's earlier this month.

Burundi has been mired in a year-long crisis in which more than 450 people have been killed since Nkurunziza pursued and won a third term. Opponents said his move violated the constitution and a deal that ended a civil war in 2005.

The central African country has an ethnic Hutu majority and Tutsi minority.

Zeid said while the number of Burundians killed had fallen since April, cases of arbitrary arrests, detention and torture had continued while ex-officers of the defunct armed forces, or FAB, had been killed because of their Tutsi ethnicity.

"I am alarmed by the very real prospect of an escalation in ethnic violence," he said.

"In the south of the country, I have also been informed of speeches by members of the Imbonerakure amounting to incitement to violence against political opponents, with strong ethnic overtones," he added, referring the ruling party's youth wing.

Neighboring Rwanda also has a Hutu majority and Tutsi minority. In Rwanda in 1994, extremist Hutus killed about 800,000 people, mostly Tutsis but also moderate Hutus,

in a genocide after years of civil war.

Burundi's government rejected Zeid's accusations, saying his report to the U.N. Human Rights Council meeting in Geneva omitted a lot of other items and was imbalanced.

"We would like to remind the council that the Imbonerakure are just members of the youth league of the CNDD-FDD, just like any other party in Burundi that has a youth component in its organization. Their stigmatization, through the different reports and statements, has cost a lot of lives," Burundian Human Rights Minister Martin Nivyabandi said.

"It's scandalous that the report does not mention young people who have tried to create chaos, after being recruited, trained and armed. There serious attacks with heavy weapons... murders by non-identified actors against members of defense and security forces - we don't really see it in this report."

Early this month, 530 students were sent home from schools across the central African country for defacing Nkurunziza's portrait, and in one incident, police shot and wounded another as they demonstrated against the arrest of fellow students.

"I am dismayed by continuing reports of the suspension and arrest of school children and students for having scribbled on pictures of the president in textbooks," Zeid said.

(Writing by George Obulutsa; Editing by Mark Heinrich)