The United States on Monday pledged $60 million to shore up a Sahel region counter-terrorism force but rejected appeals from African leaders and France to give the United Nations a supporting role.
US Secretary of State Rex Tillerson announced the bilateral funding as the Security Council met to discuss how to drum up international support to the force set up by Burkina Faso, Chad, Mali, Mauritania and Niger, known as the "G5".
"This is a fight we must win, and these funds will play a key role in achieving that mission," Tillerson said in a statement.
Washington has previously expressed support for the force, and has troops and drone operators in the region supporting operations against Islamist militants. But it opposes United Nations involvement.
"We believe that the G5 force must be first and foremost owned by the countries of the region themselves," US Ambassador Nikki Haley told the council, adding that G5 members must take on "full regional ownership" of the force.
"This is the approach that will be most effective in the end in freeing the region of terror," said Haley.
The US ambassador also rejected proposals to allow the large UN peacekeeping mission in Mali, MINUSMA, to help the joint force, saying its resources must not be overstretched.
She appeared to dismiss a proposal by UN Secretary-General Antonio Guterres to set up a UN office in the Sahel that could provide some oversight to the operations, notably to safeguard human rights.
"We also have serious and well-known reservations about using UN resources to support non-UN activity," said Haley.
Earlier the council heard the foreign ministers of France and Mali, as well as African Union Commission chairman Moussa Faki Mahamat appeal for multilateral aid to help the countries bolster their security.
French Foreign Minister Jean-Yves Le Drian said multilateral backing would be "an important signal of support from the international community to the G5 countries in their struggle against terrorist organisations."
Mali's Foreign Minister Abdoulaye Diop said funding through the United Nations would be "the only option that would guarantee a predictable and sustainable" flow of resources for the force's joint operations.
"Half-measures will not be sufficient," warned Mahamat.
The vast Sahel region has turned into a hotbed of lawlessness since chaos engulfed Libya in 2011, the Islamist takeover of northern Mali in 2012 and the rise of Boko Haram in northern Nigeria.
Earlier this month, militants with suspected links to the Islamic State group ambushed and killed four US soldiers on a reconnaissance patrol with Nigerien soldiers near the Niger-Mali border.
The UN peacekeeping mission in Mali has lost 17 peacekeepers killed in attacks this year, one of the highest tolls from current peace operations.
Guterres told the council that strong political and material support for the force was "indispensable" and said the United Nations could quickly mobilise to help the G5.
In a report sent to the council this month, the UN chief laid out four options for UN support, from setting up a UN office for the Sahel to sharing resources from the large UN mission in Mali.
The United States, which is the UN's number one financial contributor, appeared to reject all four options.
Washington's refusal to lend UN backing for the Sahel force comes after the US administration negotiated a $600-million cut to the UN peacekeeping budget this year.
The price tag for the G5 force's first year of operations is estimated at 423 million euros ($491 million), even though French officials say the budget can be brought down closer to 250 million euros.
Prior to the US pledge of $60 million, only 108 million euros had been raised, including 50 million euros from the five countries themselves. A donor conference will be held in Brussels on December 14.