U.N. Secretary-General Kofi Annan, on his first visit to the U.N. tribunal investigating Rwanda's 1994 genocide, said Tuesday he hoped the world had learned that mass killers will not go unpunished.

"I hope the message that comes out of this court, to the entire African continent and beyond, that the days when one was . . . getting away when you killed hundreds, thousands, are over, that impunity is not going to be allowed to stand," he said.Annan, the first sub-Saharan African to lead the United Nations, is on an eight-nation African tour. He said he was moved by his courtroom visit and meetings with tribunal judges and staff.

The secretary-general was in the court when a former military commander asked the International Criminal Tribunal for Rwanda to drop an indictment against him on charges of genocide and crimes against humanity.

Anatole Nsengiyumva, 47, served as commander of military operations in the western Rwandan town of Gisenyi, where he is accused of presiding over a meeting in which he ordered Hutus to organize the killing of Tutsis.

Annan said he was reassured that "with determination, justice can be done."

"I have always said that in the case of Rwanda, unless we bring the accused to trial, unless we offer justice, the healing will not begin, and reconciliation will become much more difficult."

More than 500,000 Rwandans, mostly minority Tutsis, were slaughtered in a three-month genocide orchestrated by Hutu militants that began April 6, 1994.

Since its founding in 1994, the international tribunal for Rwanda has indicted 35 people. Twenty-three are in custody.