African Union peacekeepers presently stationed in Darfur have failed to prevent the violence, Annan told delegates from Sudan, the US and the European Union who met to discuss Darfur in Brussels on Tuesday.
"I still am hopeful that we will get the Sudanese government to co-operate and to support the [proposed] force because after all we are going there to help the government, we are going to help them protect their own people," Annan told reporters.
The US and the EU have said a UN peacekeeping force is the best way to prevent more violence in Darfur.
Under-equipped and poorly-trained troops from African Union countries have proved unable to stop fighting in the vast Darfur region.
Jendayi Frazer, the US assistant secretary of state for Africa, said: "To protect innocent lives in Darfur we need an international peacekeeping operation with the capability to address the complexity of the challenges."
Violence between Khartoum-backed militias and Darfur's native inhabitants has killed as many as 200,000 people and driven 2.5 million into exile since 2003.
Sudan's delegation to the talks rejected the proposed UN force on Monday.
Women rest in a market place in a village in northern Darfur
The African Union wanted to hand over operations to the UN at the end of September, but it is short of funds.
Eight leading aid agencies have asked Western nations to give more money to the AU so that its 7,000 troops in the region can continue to operate until the UN peacekeeping force arrives.
Existing funds will run out in August. Maintaining the force after that will need at least $28.84 million per month.
Denis Caillaux, secretary-general of Care International, said: "While an enormous amount of money is being spent debating what will happen in six months time, no one seems to have noticed that people are still being killed today."
The agencies said the AU would need more money regardless of whether Sudan agrees to the UN force.
The EU will give another 40 million euros for humanitarian aid in Darfur, a European Commission official said.
Frazer, the US representative, said Washington still hoped to transfer peace-keeping duties to the UN at the end of September.
Violence first erupted in Darfur in 2003 after Darfur's native inhabitants took up arms against Sudan's government accusing it of neglect.
Khartoum responded by arming militias, known as the janjawid, which today stand accused of murder and looting.