* Some rebels ready to lay down arms
* CAR government offers power-sharing deal
* Residents fear rebel assault on capital
* U.S. calls on rebels to ensure safety of civilians (Adds U.S. State Department, paragraphs 12-15)
By Ange Aboa
BANGUI, Dec 31 (Reuters) - Rebels in Central African Republic are split over whether to start peace talks with President Francois Bozize or carry on an assault to overthrow him, a spokesman said on Monday, leaving efforts to end the conflict hanging in the balance.
The Seleka insurgents had advanced to within 75 km (45 miles) of the mineral-rich country's capital Bangui and threatened to seize the city - until Bozize made a last ditch offer on Sunday to hold talks and share power with them.
"At the moment there are divisions within Seleka on this point," said Nelson Ndjadder, a France-based official for CPSK - one of the three main rebels movements in the Seleka alliance.
"Some want to keep fighting, but CPSK is ready to put down its weapons and talk," he added.
Regional neighbours and CAR's former colonial ruler France have urged both sides to end the revolt in one of Africa's most conflict-prone regions, and the United States on Monday expressed fresh worry about the situation.
Their hopes appeared to take a hit earlier on Sunday when another Seleka spokesman, Eric Massi, said the group had rejected Bozize's proposal. But Ndjadder told Reuters Massi was not speaking for all of Seleka's fighters.
Bangui residents, who have watched the rebels edge closer in three weeks of fighting, said they were still hoping for a deal.
"We are in fear and sadness because the war has stopped everything," said Germaine Panika, a 24-year-old history student in the ramshackle riverside city. She added she would spend New Year's Eve indoors because of a military curfew.
"All we want is for the people who are fighting to solve their problems without guns," said Felix Camere, a 45-year-old teacher. "It is ordinary people who are suffering from this crisis and we're tired," he told Reuters.
Seleka unites three rebel groups - CPJP, UFDR and CPSK - who have accused Bozize of reneging on a 2007 peace deal to give former fighters money in exchange for laying down their arms.
In Washington, U.S. State Department spokeswoman Victoria Nuland said the United States is "deeply concerned about the deteriorating security situation."
"We call on the rebel alliance to cease hostilities and movements towards the capital. We also call on the rebels to ensure the safety of the civilian population," Nuland said in a statement.
"We urgently call on the CAR government to ensure that its security forces respect the human rights of the Central African people and foreign populations within the CAR," Nuland added.
Nuland said the United States is particularly concerned by allegations of "arrests and disappearances of hundreds of individuals who are members of ethnic groups" with ties to the Seleka alliance. "Those guilty of violations and crimes under international law must be held to account," Nuland said.
Central African Republic is one of a number of countries in the region where U.S. special forces are helping local forces track down the Lord's Resistance Army, a rebel group which has killed thousands of civilians across four nations.
Chad and other neighbours agreed to send 360 troops to shore up CAR's army after a string of defeats this month.
The Economic Community of Central African States (ECCAS) already has more than 500 peacekeepers in CAR which, despite rich deposits of uranium, gold and diamonds, remains one of the least developed nations on the planet.
"Their mandate will be to secure the ceasefire between the rebels and the army," said the peacekeeping mission's commander Maurice Ntossui Allogo. He said 120 troops from Republic of Congo had arrived on Monday, and 240 soldiers from Gabon and Cameroon were due in the days to come.
Chad President Idriss Deby, who is also CEEAC's president, said on Monday the force could be used if rebels move past the town of Damara, some 75 km (45 miles) outside Bangui.
"The town of Damara is a red line that can't be crossed for any reason," he said.
The streets of Bangui were unusually quiet - many residents have fled by car or boat to neighbouring Congo.
Soldiers with automatic rifles patrolled the streets and manned checkpoints while troops in French military uniform were deployed at strategic sites, including the Presidential Palace, a Reuters correspondent said.
France has reinforced its military presence in Bangui to around 600 soldiers from 150 in recent days, but says the force is to protect some 1,200 French citizens and other interests in the country, and not to defend Bozize. (Additional reporting by Nicholas Vinocur in Paris, Richard Valdmanis in Dakar, Paul-Marin Ngoupana in Bangui, Madjiasra Nako in N'Djamena and Arshad Mohammed in Washington; Writing by Richard Valdmanis; Editing by Andrew Heavens and Will Dunham)