West African neighbors of Mali are poised to impose crippling sanctions on the volatile country, whose military coup leaders on Monday missed a deadline to begin handing back power to civilians.

Representatives from the Economic Community of West African States, or Ecowas, said they would decide what action to take at a meeting in Senegal later in the day. Coup leaders had tried to stall any action by promising to hand back power on Sunday.

The standoff arose as rebels from the Tuareg ethnic group in Mali's northern desert forced another humiliating loss on government troops Sunday, seizing the historic city of Timbuktu. It was the third straight day that a regional center fell into rebel hands.

In a bid to prevent sanctions, the coup leader, Capt. Amadou Sanogo, promised late Sunday to reinstate Mail's Constitution, hours before a deadline set by Ecowas to start ceding power.

Apart from announcing the restoration of the 1992 Constitution they have not set out any timetable to hand over power to a democratically elected government in Mali, Remi Ajibewa, Ecowas head of political affairs and international cooperation, told Reuters. Captain Amadou Sanogo and his group are just buying time. 

The presidents of Ivory Coast, Niger, Benin, Burkina Faso and Liberia threatened Mali with crippling sanctions -- including closing trade borders, diplomatic isolation and a freeze in funding from the regional central bank -- if the military junta continues to cling to power.

Mali's president, Amadou Toumani Toure, was overthrown during a nighttime coup last month, amid frustration over his handling the Tuareg rebellion. Toure had already announced he wouldn't run in the April presidential election, but advances by the northern rebels were too much for the country's military to abide.

Toure's whereabouts aren't known, but he said during an interview on French radio last Wednesday that he was still in the country and safe.

The Tuareg movement is said to contain Islamic factions, a claim denied by the secular National Movement for the Liberation of the Azawad.

Despite their military successes, leaders from the rebel movement said they had no intention of pushing further south. Our aim today is not to go beyond the borders of Azawad, Hama Ag Mahmoud, a member of the MNLA's political wing, was quoted by Reuters as saying. We don't want to give anyone the impression that we are war-mongers so, once we have freed the areas we target, the job is done.

There were reports Monday that black flags identified with the Islamist movement Ansar Edine, which seeks to impose Islamic sharia law throughout Mali, were flying in Kidal and Gao, the two regional capitals that rebels captured before Timbuktu. In Kidal, music has been banned from the radio and people were no longer allowed to wear Western-style clothing, Reuters reported.