* Ban presents three logistical support options for Mali war
* UN Security Council authorized African force in December
* Ban says UN combat support could put UN personnel at risk
U.N. chief Ban Ki-moon warned the U.N. Security Council against requiring the world body to provide logistical support for combat military operations in Mali, saying such a move would put U.N. civilian staff throughout the region at "grave risk."
The 15-member Security Council in December authorized in December the deployment of an African-led military force to help defeat al Qaeda and other Islamist militants in northern Mali and called on the secretary-general to submit funding options.
Then earlier this month France launched air strikes to halt a surprise Islamist offensive toward the Mali capital Bamako and has urged an acceleration of the deployment of the African force - known as AFISMA - to back up its 2,150-strong ground forces.
"The situation in Mali is critical. Terrorist organizations threaten the way of life of the Malian people, and even the existence of the state," Ban told the Security Council in a letter on Sunday to the council, obtained by Reuters on Tuesday.
In the letter Ban presented three options for funding AFISMA - bilateral logistical support without U.N. funding; complete U.N. logistical support for all phases of the operation that would be funded through states' mandatory U.N. contributions; or bilateral support for combat phases followed by U.N. support for the deployment and stabilization.
However, he tried to steer the council away from approving the second option of full U.N. logistical support.
"If the United Nations were to provide logistics support to military forces engaged in an offensive operation, it would place civilian United Nations personnel at grave risk, and undermine their ability to carry out their current tasks in the region," Ban wrote.
The perceived neutrality of U.N. staff in Mali politics would be undermined if the world body supported the offensive.
"A dramatic shift in the posture of the (U.N.) organization would have a further negative impact on its ability to implement essential mandates in the humanitarian, development and human rights areas," he said.
'GREAT OPERATIONAL CHALLENGES'
The aim of the intervention is to prevent northern Mali from becoming a launchpad for international attacks by al Qaeda and its local allies in North and West Africa. Fears of this increased sharply after a hostage-taking raid by Islamist militants last week on a gas plant in Algeria.
Chadian forces advanced towards the Malian border on Tuesday as an African troop deployment and a U.S. military airlift swelled international support for French operations against the Islamist rebels.
Ban said that if the council decided to approve the second option of full U.N. logistical support for the African force in Mali it would take a minimum 120 days "to implement the full range of services under the logistics support package."
When the council approved the AFISMA force in December, the force - expected to eventually be around 3,300 strong - had not expected to be ready for deployment before September.
"The acceleration of the deployment of AFISMA clearly possess great operational challenges," said Ban, adding that "significant external support" was urgently required for the training, equipment, combat logistics and other needs.
Once viewed as an example of democratic progress in Africa, Mali was plunged into chaos in March by a coup that toppled the president and left a power vacuum that was quickly exploited by rebels to seize the country's desert north.
The crisis has also exacerbated a humanitarian crisis in the Sahel - a belt of drought-stricken land spanning nearly a dozen impoverished countries on the southern rim of the Sahara from the Atlantic Ocean to the Red Sea.