Protesters demanding an end to conflict in Sudan's Darfur region have been staging a day of global demonstrations.
Rallies and silent protests are taking place around the world
Activists rallied in several major cities, calling on Sudan to allow UN peacekeepers into Darfur, where tens of thousands of people have been killed.
In London, there was a rally outside the Sudanese embassy, while thousands protested in New York's Central Park.
Khartoum has dismissed the protests, saying those taking part have been misled by the international media.
Up to two million people have been displaced in three years of conflict in Darfur.
The US and France have both said a genocide is taking place, with the US directly accusing Khartoum of responsibility.
On Saturday UK Prime Minister Tony Blair wrote to leaders of the European Union, calling the situation in Darfur "unacceptable" and urging them to take a common stand on the issue.
Rallies took place in some 30 cities around the world.
Among those involved were the South African Archbishop Desmond Tutu and Canadian General Romeo Dallaire, who headed the UN peacekeeping force in Rwanda during that country's genocide in 1994.
About 20,000 people gathered in Central Park to press the US government for action.
Former US Secretary of State Madeleine Albright said: "The world must act and it must do so now because time is not on our side."
BBC world affairs correspondent Mike Wooldridge says the issue is likely to be a key one at this week's UN General Assembly.
In Cambodia, devastated by the Khmer Rouge genocide in the 1970s, a candle-lit vigil was held in the capital, Phnom Penh.
Speaking ahead of the protests, Sudan's junior foreign minister, Ali Karti, said the demonstrators were misunderstanding the situation in Darfur.
"Unfortunately, the people there in the West, in Europe and the United States are moved by the media and the media is unfortunately moved by political agendas," he said.
Khartoum says it is defending the territorial integrity of Sudan against rebels backed by neighbouring Chad.
Steve Ballinger, a spokesman for Amnesty International, rejected Mr Karti's interpretation of events.
"The situation is dire already in Darfur, and it is only going to get worse when the African Union troops leave at the end of this month, unless the UN peacekeeping mission is allowed back in," he said.
Seven thousand African Union peacekeeping troops are due to leave Darfur at the end of September, but Khartoum has refused to allow UN peacekeepers to take their place.
The government has stressed that any UN troops entering Darfur would be met with armed resistance.
On Saturday 1,000 volunteers from a pro-government militia marched through the streets of Khartoum threatening to kill any uninvited UN visitors, the BBC's Jonah Fisher reports from the city.
Violence in the region is reported to be rising again, drawing criticism from figures as diverse as the UN Secretary General, Kofi Annan, and actor George Clooney, who this week implored the UN Security Council to act.