It comes as US deputy secretary of state John Negroponte accused the Sudanese government of backing the janjaweed militia, which has been blamed for numerous atrocities in the region including rape, arson and looting.
Oxfam says the conflict has brought about the "greatest concentration of human suffering in the world" and blames the international community for allowing the conflict to spread, "blighting the lives of some four million people and forcing many to the very brink of survival".
The charity says it is currently providing aid to 530,000 people, of which 470,000 are in Darfur and 60,000 are in neighbouring Chad, which has also been affected by the conflict.
"In Chad, the number of people forced to flee their homes has doubled in just four months," Penny Lawrence, Oxfam's international director, said.
"This is an outrage that affronts the world's moral values. We once more need the support of the British public to show that the world cares and help Oxfam to continue to keep people alive."
According to Oxfam, more than two million people have been displaced in Darfur and are living in refugee camps. Four million are dependent on humanitarian aid, of which one million are not receiving what they need.
In Chad, 375,000 people are said to have sought shelter from armed conflict and 140,000 of the country's citizens have been displaced, in addition to the 250,000 Sudanese refugees who have already arrived in the east of the country looking for help.
"Despite a level of attention to the crisis international political inertia has meant that there has been little effective progress towards a peaceful solution. Greater international efforts are needed," Ms Lawrence added.
"Meanwhile the millions of innocent people caught up in this outrage cannot wait for the politicians to agree. They need to be kept alive while the political inertia continues."
Meanwhile, following a three-day tour of Sudan, Mr Negroponte urged the country's government – which denies supporting the janjaweed militia – to do more to stem the violence.
"The government of Sudan must disarm the janjaweed, the Arab militias that we all know could not exist without the Sudanese government's active support," he said.
He also called on the rebel groups who did not take part in last May's Darfur Peace Agreement to "come to the negotiating table" and accused the government of "creating the impression that the government of Sudan is engaged in a deliberate campaign of intimidation" by denying visas and engaging in "harassment" of international aid workers.
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