Speaking at a meeting organised on the sidelines of the UN General Assembly, Ms Rice said time was running out.
She hinted that, should Sudan continue to refuse access to UN peacekeepers, "other measures" were available.
Sudan's government vehemently opposes such a force, arguing that there is a hidden agenda to weaken the country.
"The violence in Darfur is not subsiding, it is getting worse," Ms Rice said.
By Richard Allen Greene in Washington, BBC News
As France continues the probe into 'Bin Laden death' leak and US-bashing proves popular pastime at UN, the BBC's Richard Allen Greene in Washington writes that George W Bush's presidency is already over.
"You can see it on the T-shirts, such as the one that simply says: "20 January 2009", the day Mr Bush will step down and hand power to whoever wins the 2008 election.
"While his foes dream of the day Mr Bush's term actually ends in two-and-a-half years, it may already be essentially finished for all practical purposes."
Tens of thousands protest against Blair
By Adrian Croft, Manchester, Reuters
Tens of thousands of protesters marched on Saturday against Prime Minister Tony Blair on the eve of a rally of his Labour Party where a struggle over the leadership looked set to steal the headlines.
Activists shouting "Blair must go!" and chanting opposition to the Iraq war and to nuclear weapons streamed through the centre of the Manchester, which will host Labour's annual conference from Sunday until Thursday.
It will be Blair's final conference as party leader after nine years in office and three successive election victories.
At a time when violence sweeps Iraq on Ramadan, Blair's backing for the U.S.-led war on Iraq, his policies in the Middle East and his reforms of public services have angered many in Labour, leading to a slide in his popularity.
Blair's sister-in-law, Lauren Booth, fronted one of the anti-war demonstrations, saying it was a "massive embarrassment" to be related to the prime minister and urging him to resign.
Police estimated the number of protesters at around 20,000 and said there had been no arrests by mid-afternoon. Organisers said tens of thousands more had taken to the streets.
Chancellor Gordon Brown has been waiting for years to succeed Blair and Brown ally Ed Balls, widely thought to be a future finance minister if Brown becomes leader, gave a flavour of a Brown premiership, saying he would be a tough negotiator.
"What we will see is Brown the tough negotiator who will stand up for Britain's interests, who's willing to say 'No' when 'No' is the right thing to say," he said.
Hezbollah head praises 'victory'
The Hezbollah leader, Sheikh Hassan Nasrallah, has hailed his group's "victory" over Israel, boasting that the group still has 20,000 rockets.
Calling for a new Lebanese government in his first public appearance since the recent conflict, he said Hezbollah would never be disarmed by force and would only disarm when the Lebanese government was capable of protecting the country.
Hundreds of thousands crowded into southern Beirut, heavily bombed during the conflict, to hear the speech.
The strength of Hezbollah had dealt a severe blow to US plans for a new Middle East peace process, he told the crowds.
Israel lost 116 soldiers in the fighting, while 43 of its civilians were killed in Hezbollah rocket attacks.
More than 1,000 Lebanese civilians and an unknown number of Hezbollah fighters were killed in the conflict.
Israel failed to achieve its stated war aims of driving Hezbollah fighters from the border, stopping rocket attacks and freeing two of its soldiers captured by Hezbollah in a cross-border raid.
Pictures courtesy of BBC News online.