More than 2,000 people died in ethnic clashes in Sudan last year
Campaigners have kept up a drum beat opposite Downing Street to urge the government to do more to prevent bloodshed in Sudan.
So-called "Beat for Peace" events are being held in 15 countries on Saturday.
Drummers from bands like Pink Floyd have also made a film, warning that Sudan could return to the civil war which killed millions of people.
Gordon Brown has pledged to "step up" the UK's role in peacekeeping and development in the country.
Five years ago a peace deal was signed ending Sudan's 22-year-long civil war.
But violence flared again in 2009, with more than 2,000 people killed and 350,000 displaced in south Sudan.
Campaigners now fear the country could slide back into all-out war unless world leaders do more to try to bolster the fragile peace agreement.
'Insecurity and poverty'
Scores of activists gathered opposite Number 10 on Saturday, beating drums and waving banners saying, "UK don't forget Sudan".
Sudanese Archbishop Daniel Deng was due to address the gathering ahead of a meeting with Mr Brown on Monday.
International Development Minister Gareth Thomas told the rally that the British government would continue to work to sustain peace in Sudan.
In a statement, the prime minister said: "Sudan's recent history has been one too often marked by violence, insecurity, and poverty for its people.
"Sudan's leaders - with the support of the international community - must not allow this also to be the story of Sudan's future."
A referendum is due to be held in January 2011 on independence for the south, but campaigners fear a return to conflict this year could put that vote at risk.
The Beat for Peace film, part of the broader Sudan365 campaign, features drummers from bands like Radiohead, The Police and Snow Patrol, alongside musicians from Sudan and other countries, including Japan and Australia.
Another of the bands taking part is Faithless and one member, Jamie Catto, told the BBC why he wanted to get involved.
"My personal connection with Sudan is my personal connection with humanity," he said.
"There's nothing else to do but take urgent action and make sure the powers that be listen."