The world must be ready to impose sanctions on Sudan if it reneges on its pledge to let more peacekeeping forces into ravaged Darfur, Secretary of State Condoleezza Rice said Monday.

The Sudanese government has finally agreed to a larger force aimed at stopping four years of killing. But Rice sounded a note of caution amid bland or optimistic assessments by other nations.

"Sudan has a history of agreeing to things and then trying to condition or change them or to backtrack and say, 'Well no, we didn't really agree to that,"' Rice said at a conference on Darfur organized by the new conservative-led French government.

The conflict began when African rebels in Sudan's arid Darfur region took up arms against the central Sudanese government more than four years ago, accusing it of decades of neglect. Sudan's government is accused of unleashing in response a militia of Arab nomads known as the janjaweed — a charge Sudan denies.

"We have lost a lot of time while agreements have been made that have not been kept," Rice added. "We can no longer afford a situation in Darfur where agreements are made and not kept."

The U.N. chief, Ban Ki-moon, insisted at the meeting that "slow but credible and considerable progress" has recently been made to resolve the crisis.

President Bush announced more U.S. sanctions on Sudan last month, but at Ban's request the U.S. held off on pushing hard for broader United Nations punishments. Possible punishments would target Sudanese officials and companies, or companies doing business with the oil-rich African nation.

Sudan initially accepted the plan in November but then backtracked, before finally agreeing earlier this month. The timing was interpreted as an attempt by Sudan's leader, President Omar al-Bashir, to avert U.N. sanctions and take the sting out of the conference held Monday in Paris.

"The United States will continue to argue that there must be consequences for Sudan if it does not live up to the obligations that it has undertaken," Rice said. Washington supports Ban's diplomatic efforts to bring Sudan along, Rice said, "but there is a history here."

"Until Sudan has actually carried out the commitments that it has taken, I think we have to keep the possibility of consequences on the table," she added.

Apart from that, Sudan's Arab-led government in Khartoum came in for almost no criticism at a press conference held by some of the diplomats who attended the session, and al-Bashir was not rebuked by name over the conflict that has killed more than 200,000 people since 2003. Another 2.5 million have become refugees.

Although the U.N.'s Ban did not talk of sanctions, he also said Sudan must follow through on its commitments and urged rebel leaders to show "flexibility and political leadership."

"This time is for action, particularly by President Bashir," he said.

The United Nations and Western governments pressed Sudan for months to accept a plan for a large joint force of U.N. and African Union peacekeepers to replace the overwhelmed 7,000-strong African force now in Darfur.

Rice said the switch must happen "as quickly as possible."

"We can't afford to wait," she said.

But many questions remain on how and when the troops will be deployed and how they will be funded. Those questions were not answered Monday, and there were no specific accomplishments announced after the session.

While the United Nations wants the planned hybrid force to keep its "African character," it may need to look beyond Africa for specialized troops — such as doctors and engineers — and for equipment, said U.N. peacekeeping official Jean-Marie Guehenno. The U.N. special envoy to Darfur, Jan Eliasson, said his native Sweden as well as neighboring Norway were offering engineer units.

The United States and others have considered a separate U.N. resolution to lend structure for the new force.

French Foreign Minister Bernard Kouchner said Monday's session was not intended to be a peacemaking conference, and Sudan's government was not invited. Rice said the session allowed participants to "take stock" of the complicated conflict and diplomacy.

Kouchner said the group, which included Sudan's significant trading partner and diplomatic protector China, would meet again in the fall.

China again came out against sanctions and argued against appeals by some critics for a boycott of the 2008 Beijing Olympic Games to force China to get tough with Khartoum.

"Now is not the time to talk about further sanctions," said China's special envoy for Sudan, Liu Giujin. He said any attempted link to the Beijing Olympics was "really unfounded. The basic character of the Olympics is nonpolitical."

Eliasson, the U.N. Darfur envoy, said he would count on China's cooperation.

"China has already played a constructive role in terms of influencing or sending the message to the government of Sudan that they indeed should accept a larger UN presence, like the hybrid force. I know China was fully behind that," he said.

Kouchner said the existing, small, African Union force in Darfur is badly equipped and unpaid.

"We are not going to make progress by increasing the number of soldiers who are unpaid," Kouchner said.

French President Nicolas Sarkozy pledged an additional $13.4 million to the existing cash-strapped African Union force. His five-week-old government has made the conflict in Darfur a priority. Spain pledged $13.4 million, with half for the hybrid force and the rest for humanitarian aid. The European Union's development chief, Louis Michel, said it was preparing $40 million in additional humanitarian aid.

Sarkozy, speaking to the conference delegates before their meeting, decried the world's inactivity on Darfur and called for a firm stance against "belligerents who refuse to join the negotiating table."

"Silence is killing," he said. "The lack of decision and the lack of action is unacceptable."