By Mathieu Bonkougou and Nadoun Coulibaly
OUAGADOUGOU, Nov 3 (Reuters) - Burkina Faso's army will quickly cede power to a transitional government and appoint a new head of state, the country's interim President Isaac Zida said on Monday, looking to calm accusations that the military had seized power in a coup.
Longtime president Blaise Compaore stepped down on Friday following two days of mass protests in the impoverished West African nation over his bid to extend his 27-year rule by amending the constitution.
On Saturday, the military appointed Lieutenant Colonel Zida as provisional head of state, drawing criticism from opposition politicians, the African Union and Western powers who want to see a swift return to civilian rule.
The African Union, whose democratic charter binds its 54 member states to take action against coups on the continent, plied more pressure on the Burkina military on Monday, giving it an ultimatum to hand back power to a civilian administration within two weeks or face sanctions.
The United States which could freeze military cooperation with Burkina Faso if it deems a coup has taken place, said on Monday it was not ready to determine whether the takeover by the army amounted to a coup.
Zida told a gathering of diplomats and journalists in the capital Ouagadougou that executive powers would be passed to a transitional government, in accordance with the constitution.
"We are going to move very fast, but be careful not to commit a mistake that might damage our country," he said.
"We are not here to usurp power and to sit in place and run the country, but to help the country come out of this situation," Zida said, adding that a new head of state would be chosen following broad discussions with various groups.
His announcement came in the wake of crisis meetings late on Sunday and Monday between Zida and opposition leaders after thousands gathered to denounce his appointment in the central Place de la Nation - the scene of violent protests last week during which the parliament was set alight.
The head of the United Nations Office for West Africa Mohamed Ibn Chambas said a joint mission which comprises the U.N., the A.U. and regional bloc ECOWAS, was pursuing talks with the all the parties in the crisis.
"The joint mission is encouraged by the commitments of the parties to work together for the organization of a transition in accordance with the constitution," Chambas said in a statement.
Ghana's president and ECOWAS current chairman John Dramani Mahama is expected in Burkina Faso on Wednesday to hold further talks with the parties, Kadré Désiré Ouédraogo, ECOWAS commission president told journalists in Ouagadougou.
Equatorial Guinea's Ambassador to the African Union, Simeon Oyono Esono, who holds the rotating chair of its Peace and Security Council, told journalists in the Ethiopian capital that although popular pressure led to the ousting of Compaore, the change had been undemocratic.
"We have taken note of the origin of the popular revolt which led to the military getting power, so we determined the period of two weeks and after that period we are going apply sanctions," Esono said.
Under Burkina Faso's constitution, the head of the National Assembly should take office if the president resigns, with a mandate to organize elections within 90 days. However, the National Assembly head has reportedly fled the country, along with other senior figures from the Compaore administration.
Compaore himself arrived in neighboring Ivory Coast on Saturday, the government there said in a statement.
Burkina Faso troops cleared thousands of protesters from the capital and opened fire at state TV headquarters o
n Sunday, killing one person, after crowds had flocked there in anticipation of the announcement of a new leader.
Calm had returned on Monday, with banks reopening and traffic beginning to fill up the dusty streets of the capital. An overnight curfew remained in place.
Zida's appointment marks the seventh time that a military officer had taken over as head of state in Burkina Faso since it won independence from France in 1960. It was previously known as Upper Volta.
Benewende Stanislas Sankara, a member of the opposition party UNIR/MS, expressed concern at the army's role in overseeing governance. "Nobody can place their confidence in the army. But the military authorities in power now appear to be acting in good faith," he told Reuters.
(Additional reporting by Aaron Maasho in Addis Ababa and Bate Felix in Dakar; Writing by Emma Farge and Bate Felix; Editing by Daniel Flynn and Dominic Evans)