"In front of all Burundians, I, Pierre Nkurunziza, swear that I will always respect the Burundian constitution and the peace agreement," he said, touching the Burundian flag with one hand and placing another on the copy of the constitution.
"I swear to ban all ideologies of ethnic division and genocide. I swear to work for the development of all Burundi."
Nkurunziza's inauguration on Friday after a series of democratic polls was a huge step forward for the small central African nation, battered by war, ethnic division and poverty that forces many of its seven million people to survive on as little as 25 cents a day.
Securing peace in Burundi is seen as crucial to overall stability in the volatile Great Lakes region, racked by ethnic conflict, fights over resources and refugee problems.
Second elected president
The former physical education lecturer, whose narrow escape from death at the hands of rampaging Tutsi soldiers turned him into a guerrilla fighter in 1995, became only the second elected Hutu president in Burundi's post-independence history.
He was sworn in briefly in Burundi's legislature, in front of dignitaries including the presidents of South African, Rwanda, Tanzania, Kenya, Ethiopia and Mozambique.
"I swear to ban all ideologies of ethnic division and genocide. I swear to work for the development of all Burundi"
Lawmakers sitting as an electoral college elected the devoutly religious 40-year-old Nkurunziza a week ago in a vote that was a foregone conclusion as he was the only candidate.
His guerrilla movement-turned-political party, the Forces for Defence of Democracy (FDD), dominated elections to the legislature held under Burundi's UN-backed 2000 peace plan, on a platform of restoring democracy and ethnic inclusion.
Some opposition groups accuse Nkurunziza of war crimes, and a Tutsi government sentenced him to death in 1999 for laying landmines that killed several people.