Under pressure to hand over power, the leader of a military coup in Mali said Sunday that he had reinstated the country's constitution and government institutions, as rebels continued their advance in the north.Capt. Amadou Aya Sanogo said in a statement that the coup's leaders would begin "consultations" to form a transitional government, which will be "responsible for organizing peaceful, free open and democratic elections in which we will not participate."The statement did not specify when the meetings or the elections would be held.Leaders of neighboring West African nations have condemned the coup and ordered the military junta to hand over power back to the civilian government by Monday or face sanctions.Sanogo's announcement came as rebels in Mali said they had seized control of another town in the north, Timbuktu -- a major blow to the coup leaders who toppled the nation's president last month.Residents said government soldiers withdrew from the area ahead of the attack.On Saturday, the Tuareg rebels said they seized the key town of Gao, which is hundreds of miles from the capital of Bamako.The fall of both towns marks a major prize for the fighters seeking to wrest control of the region to make it their homeland and intensifies the crisis in the West African nation after soldiers ousted the president March 22 over what they said is his inability to handle the Tuareg rebellion in the north.In a statement during the coup, they accused President Amadou Toumani Toure of "incapacity" in battling the rebels, saying he did not equip soldiers with the means to quash the growing Tuareg insurgency.Sanogo reiterated concerns over the rebels in his statement Sunday."We are very concerned about the attacks carried out by various armed groups in the north of Mali and determined to defend, whatever it costs, the territorial integrity of our country," he said.Tuareg rebels comprise different factions, including the main National Movement for the Liberation of Azawad, which claimed the seizures of Gao and Timbuktu.In the group's statement claiming control of Timbuktu, it called for dialogue with the Economic Community of West African States (ECOWAS) to help re-establish peace.The influx of Tuareg fighters returning from Libya has re-energized the insurgency, whose battles with government forces have sent tens of thousands of Malians fleeing into neighboring countries.