Military intervention in northern Mali is inevitable if talks with militant Islamists controlling the area fail, Nigeria's leader has warned.
President Goodluck Jonathan said a West African force would be deployed, but only with UN approval.
It has so far refused to endorse military intervention, saying it needed more details about the plan.Alleged atrocities committed in the rebel-held north are being investigated by international prosecutors.
Mr Jonathan said the regional body, the Economic Community of West African States (Ecowas), would "definitely" send a force to the area if a peace deal is not reached with the Islamist fighters.
"Diplomacy and negotiation is first. Military intervention is extreme," he said, during a visit to Senegal.
"When negotiations fail, at that time you can talk about military intervention."
Burkina Faso's Foreign Minister Djibrille Bas held talks with the militants last month as part of Ecowas's diplomatic effort to end the conflict.
Ecowas, at the same time, asked the UN Security Council to endorse its plan to send 3,000 troops to Mali.
However, it refused, saying it needed more clarity on the West African body's military objectives and how it intended to achieve them.
Islamist groups and Tuareg rebels took control of large swathes of northern Mali after President Amadou Toumani Toure was overthrown in a coup in March.
But the rebel alliance has since ruptured, with Islamist fighters chasing Tuareg rebels out of several northern towns and imposing Sharia law.
The Islamists have destroyed ancient shrines in the historical city of Timbuktu, claiming they violated Sharia law and promoted idolatry among Muslims.
The UN warned that the destruction of the shrines could amount to war crimes and the International Criminal Court has launched a preliminary inquiry into alleged atrocities.
The Islamists have also stoned to death an unwed couple and amputated the hand of an alleged thief.
A new unity government was formed in Mali's capital, Bamako, at the weekend, promising to spearhead initiatives to end the instability in the north.