The United Nations has failed to properly investigate the devastating truck bombing that destroyed the UN mission in Baghdad 10 years ago and killed envoy Sergio Vieira de Mello, his former partner charged Monday.

"Given the unprecedented and serious nature of the attack, what one might have hoped for was to investigate and promote activities to shed light on it," said Carolina Larriera, de Mello's colleague and lover.

"However, inaction prevailed and the few traces that surfaced about its perpetrators were ignored or sabotaged," she said in emailed responses to questions by AFP.

The bombing of the UN mission in Baghdad on August 19, 2003 was a key event in Iraq's spiral into chaos after the US invasion.

Twenty-two people were killed and 200 more injured when a suicide bomber ran a truck loaded with explosives into the Baghdad hotel housing the UN offices.

De Mello, a much admired Brazilian diplomat who was the UN secretary general's special representative to Iraq, died in the rubble of the collapsed building.

It was the first time a UN mission anywhere in the world had come under attack since the world body's founding, and foreshadowed the rising violence that drove the UN to withdraw its staff from Iraq.

Larriera, who was there, said it was "terrible."

"The day of the attack I was just a few meters away from Sergio when the bomb exploded," she said.

"I took it upon myself to find him alive in the rubble, to talk to him and to find help," she said.

And yet for years, she said, she was ignored by the United Nations, even though she was a career UN official as well as de Mello's partner.

"They didn't even include me in the list of survivors and had no interest in hearing my testimony," she said.

"It's important to me, to honor our relationship and our common projects, that there be a true, in-depth investigation," she said.

Larriera, an Argentine, said her relationship with de Mello began in violence-torn East Timor, where he was in charge of shepherding the territory's independence from Indonesia in 2002.

She later worked for him in New York when he served as UN High Commissioner for Human Rights, and then in Iraq.

She said his tenure in Baghdad was marked by increasing tensions between the UN mission and the US-led coalition that toppled the regime of Saddam Hussein.

"In our last months there, our dialogue with the coalition was nearly broken. And Sergio desperately was trying to give a multilateral dimension (to the UN mission)."

Larriera quoted Brazilian Defense Minister Celso Amorim as questioning in a recent book whether security at the mission wasn't deliberately weakened, perhaps to divert attacks from coalition targets.

"As a former official who survived the attack and Sergio's partner I can say that to this day none of the victims, survivors, family members, friends and thousands of 'in house' officials have understood the precise circumstances of the attack, the motives of the perpetrators and the penal and moral responsibility that belongs to those who permitted and made possible the attack," she said.

"Instead, they have buried the circumstances surrounding the incident with busts and commemorative speeches," she said.

She said an Iraqi who was arrested for the bombing, Awraz Andel Aziz Majmoud Said, was willing to speak about his role in the attack.

"But despite the many international requests, especially those of the Special Rapporteur on the Independence of Judges and Lawyers, he was executed before making a statement before the courts," she said.

The United Nations, asked to react to Larriera's statements, did not offer an immediate comment.