Ban yesterday expressed alarm about increasing retaliatory attacks between Muslim and Christian groups in a report which calls on the UN Security Council to act urgently on the crisis.
Rebels overthrew Central African Republic's president in March but a transitional government has lost all grip on the huge but impoverished country of 4.5 million people.
"The population lives in fear," Ban said in the report, obtained by AFP ahead of a Security Council meeting on the crisis next Monday.
Four involve providing various forms of financing and logistical support for an African force already in the country.
The fifth option is a UN peacekeeping force of between 6,000 and 9,000 troops, plus 1,700 police.
While Ban does not opt for any of the options, the report makes it clear that the African force, officially known as MISCA, even reinforced with international finance will be less effective than UN peacekeeping troops.
"When you read the report with attention, you understand that the African force will not be able to confront the crisis and that only a UN peacekeeping mission can avoid the worst case scenario," said Philippe Bolopion, Human Rights Watch's UN specialist who has just returned from a mission to Central African Republic.
The 2,500 strong African force is eventually to be increased to 3,650 troops.
But violence is already worsening in the resource-rich state where a coalition of rebels, known as Seleka, forced President Francois Bozize to flee in March.
Armed gangs, mainly consisting of former Seleka fighters, now control most of the country. But there has been an increase in clashes between Muslim groups and self-defence units formed by Christian villages.
