Rwandan President Paul Kagame has accused the international community of deliberately failing to prevent the genocide in the country 10 years ago.
Kagame: Rwandan lives "regarded as insignificant"
Speaking at the conference on the killings in the Rwandan capital Kigali, Mr Kagame condemned the worldwide inaction at the time.
He also questioned whether countries would act differently now.
Some 800,000 Tutsis and moderate Hutus were killed by Hutu militias during a few weeks in 1994.
The conference marks the beginning of a week of commemoration for the victims.
It is being attended by survivors, academics and foreigners who witnessed the killings.
On Sunday, many were taken to burial sites outside the capital to pay homage to the victims.
"The more opportunities there are to explore - not just the aspect
of the bodies and the graves but also the background - the better," Canadian visitor Gerry Caplan told AFP news agency.
In his opening speech, Mr Kagame raised the possibility that international indifference could be down to racism.
"We should always bear in mind that genocide, wherever it happens, represents the international community's failure, which I would in fact characterise as deliberate, as convenient failure," Mr Kagame told the conference.
1994: RWANDA'S GENOCIDE
6 April: Rwandan Hutu President Habyarimana killed when plane shot down
April -July: An estimated 800,000 Tutsis and moderate Hutus killed
July: Tutsi-led rebel movement RPF captures Rwanda's capital Kigali
July: Two million Hutus flee to Zaire, now the DRC
"How could a million lives of the Rwandan people be regarded
as so insignificant by anyone in terms of strategic or national
"Do the powerful nations have a hidden agenda? I would hate
to believe that this agenda is dictated by racist considerations
or the colour of the skin, I hope it is not true," said Mr Kagame, whose Tutsi-dominated rebel RPF took power in July 1994, ending the genocide.
Several speakers also accused the international community of showing indifference to the survivors of the killings, many of whom were raped and infected with HIV.
United Nations Secretary General Kofi Annan, who was head of
peacekeeping at the world body during 1994, has accepted
institutional and personal blame for not doing more
to prevent the Rwandan slaughter.
The BBC's Robert Walker in Kigali says that over the next two days, conference participants will be discussing the causes and legacy of the genocide, and what can be done to prevent similar tragedies occurring elsewhere.
On Wednesday, eight heads of state or government and other foreign dignitaries will attend a formal ceremony in Kigali stadium.
Many of the victims will be re-buried in a new memorial on Kigali's Gisozi hill.
Former colonial power Belgium is the only Western country to send its leaders.
Hutus were politically dominant before the killings
The United States will be represented by the special envoy for war crimes, Pierre-Richard Prosper.
Mr Annan is sending his special adviser on Africa, Ibrahim Gambari.
Our correspondent says the government hopes the commemorations will provide an opportunity to dignify the memory of those killed, and show the world the progress Rwanda has made in reconstruction.
Stability has been restored in Rwanda in the decade since the genocide, but Mr Kagame's government has been accused by human rights groups of using memories of the genocide to oppress its opponents.
Last month, a French report last month concluded that Mr Kagame had ordered a rocket attack which brought down a plane carrying the then Rwandan and Burundian presidents, killing both men and precipitating the massacre.
Mr Kagame denied the claim, and accused "French elements" of providing weapons to and training those who carried out the genocide.