The United Nations has marked the first anniversary of the bombing of its headquarters in Baghdad with a memorial service honoring those who were killed and injured. The top UN envoy to Baghdad, Sergio Vieira de Mello, was among 22 people who died in that terrorist attack. The ceremony in Geneva was presided over by the U.N. Secretary-General, Kofi Annan.

Family members, survivors and injured staff, led by U.N. Secretary-General, Kofi Annan, filed solemnly into the hall of the General Assembly.

In his speech, Mr. Annan said the bomb that blew up the U.N. headquarters in the Canal Hotel brought the organization face to face with a new and more intimidating form of danger.

"The danger that we, servants of the United Nations, will no longer be victims simply by virtue of the times and places in which we are called to serve, but may have become in ourselves one of the main targets of political violence," Mr. Annan said.

Mr. Annan's speech was followed by a moving ceremony in which family members of each of the 22 victims lit a candle in memory of their loved ones.

The suicide bombing caused the United Nations to pull its staff out of Iraq. The U.N. just recently re-established a limited presence there with the appointment of a new envoy. But, most U.N. officials have not returned to the country.

A U.N.-appointed investigation team criticized the organization for doing too little to protect its employees and ignoring credible evidence of danger. A separate investigation by the United States has not uncovered the identity of the perpetrators.

Prior to the ceremony, Gilda, the mother of Sergio Vieira de Mello, told reporters that she could not accept what had happened to her son.

She said she did not understand how this could happen. She said she wants truth and justice for her son who had given his life.

A survivor of the blast, Carolina Larriera, joined her voice with those of other survivors in calling for a systematic and proper inquiry. She said she had been questioned by the FBI, but had not been told the results of the investigation.

"We think the best way to honor them is just to know what happened? And not now live in this gray area where nothing is clear and where there is a lot of speculations that need not be there," she said.

Speakers at the memorial ceremony vowed that the United Nations would continue to help bring stability and peace to the many victims of war and injustice.

The ceremony ended with a musical tribute by the American soprano, Barbara Hendricks.