A senior US official said on Wednesday that although the deadline could not be met, Washington remained convinced that an agreement could be forged in the early part of the new year.
"They are really close and we're going to keep up the pressure, we're not going to let this slide," the official said. "The game is not up."
US President George Bush has made peace in Sudan a priority for his administration.
In recent weeks both he and Secretary of State Colin Powell have telephoned the principal actors to urge them to finalise negotiations to end the two-decade-old civil war.
Most recently, Powell spoke on Tuesday with Sudanese President Umar al-Bashir, vice-president Ali Usman Taha, and John Garang, the leader of the Sudan People's Liberation Army (SPLA) rebels.
Powell's message, even as the deadline neared, was "don't let this slip through your grasp", a State Department official said.
Bush spoke with al-Bashir and Garang by phone earlier this month as the talks entered their final stage with three areas - power, wealth-sharing and the status of three contested areas - left outstanding.
Al-Bashir was quoted on Tuesday as saying he expected a deal to be reached by next week.
"They are really close and we're going to keep up the pressure, we're not going to let this slide... The game is not up"
US offical on the Sudan peace talks
He noted that agreements had been reached on many contentious points and secured the two sides' commitments to reach a pact by 31 December.
Brutal civil war
The war in Sudan, which erupted in 1983, is the longest on the African continent.
It has pitted the south, where most observe traditional African religions and Christianity, against the Muslim, Arabised north.
The conflict has claimed at least 1.5 million lives and displaced an estimated four million people.
Previous rounds of talks, also in Kenya, have yielded success.
In 2002, the foes agreed that after six years of self-rule the south will hold a referendum on whether to join the north, or secede.
Meanwhile, a Sudanese opposition Islamist party said on Wednesday the government had arrested three of its leaders and 22 other members for having links to rebels in the western Darfur region.
Witnesses also said Sudanese authorities raided a Khartoum university dormitory on Wednesday and arrested 50 members of the politically active Darfur Students' Union there.
The Popular National Congress (PNC) party led by prominent Islamist Hassan al-Turabi denied any direct contact with two main Darfur rebel groups. The groups launched a revolt in February, accusing Khartoum of marginalising the remote area.
The United Nations says the Darfur strife has displaced more than 600,000 people and warns of a humanitarian crisis there.