Meetings and rallies took place at about 50 cities around the world on Sunday as part of Darfur Day.
In Rwanda, survivors of the 1994 genocide called for action to resolve the crisis in Darfur.
Freddy Umutanguha, a survivor of the genocide, said: "In 1994, the world left Rwandans to their fate and a million people were murdered. Today, the world must stop genocide in Darfur.
In London, Christian, Jewish and Muslim leaders prayed outside the residence of Tony Blair, the British prime minister.
Blair sent a letter to the European Union asking them to pressure the Sudanese government and rebels to end the conflict there.
He warned that the Sudanese government should prepare to face isolation if it failed to respond to diplomatic pressure to end the "slaughter".
In Khartoum, a small group of people staged a counter-demonstration branding the Darfur Day events a Jewish conspiracy. The demonstrators also opposed the deployment of a proposed UN peacekeeping force in Darfur.
More than 200,000 people have been killed and two million left homeless during the fighting which began when ethnic African tribes began an armed campaign against the Khartoum government.
The government is accused of supporting militias known as the Janjawid who have been blamed for widespread atrocities.