The meeting in New York will bring together leaders from U.N. Security Council and other interested countries as well as United Nations, African Union and World Bank representatives.

It is expected to focus on a January 9 referendum among the people of semi-autonomous southern Sudan on whether to become an independent country, as well as on the seven-year-old conflict in Darfur, western Sudan.

"The president sees this meeting on the 24th as a very important vehicle for focusing international attention on ... (the referendum) as Sudan approaches really the last critical 100 days before that vote takes place," Rice said.

"The meeting in New York will also send important signals to the Sudanese people," she told reporters on a conference call. "It will underscore that the international community ... expects that political leaders will rise to the challenge of addressing the difficult issues that still have to be negotiated if there's going to be lasting peace."

Earlier, U.S. Secretary of State Hillary Clinton said Sudan was a "ticking time-bomb" ahead of the vote and that the international community must redouble efforts to head off violence there.

The State Department said Clinton had telephoned Sudanese Vice President Ali Osman Taha and southern leader Salva Kiir on Wednesday. It also said that Scott Gration, U.S. special envoy for Sudan, would make a new trip to the region on Thursday to pursue talks on preparing a peaceful referendum.

In Khartoum, state news agency SUNA said Taha told Clinton that Sudan's government was committed to holding the plebiscite.

Clinton expressed her "satisfaction" with the progress toward holding the referendum, and also thanked the Sudanese government for helping to release a U.S. aid worker in Darfur last week after she had been held by kidnappers for more than 100 days, SUNA said.