NIAMEY (AFP) - The head of Nigers air force has been arrested on suspicion of involvement in an alleged plot for which other senior officers were held last month, a government source said Wednesday. The source said Colonel Hassane Mossi, a member of the ruling junta, had been arrested on November 16 and was being held in police custody. Four senior officers, including the former deputy head of the junta, were arrested in mid-October and accused of plotting to assassinate head of state General Salou Djibo and stop his planned transition to civilian rule. The junta, called the Supreme Council for the Restoration of Democracy took power in a coup on February 18 that ousted president Mamadou Tandja after he tried to cling to office. But it won widespread support when it pledged to turn the poor west African country, which ranks last on the Human Development Index, into a beacon of good democracy and governance. The transition to civilian rule began with a referendum on October 31 on a new constitution which was overwhelmingly backed. Local elections and a presidential poll are planned for January 31, with the new president to be sworn in on April 6, 2011. The four arrested in October amid rumours of a coup were Colonel Abdoulaye Badie, the former number two in the junta, former equipment minister Colonel Amadou Diallo, Lieutenant Colonel Abdou Sidikou, and Lieutenant Colonel Sanda Boubacar. The government source said they had recently been moved from the paramilitary gendarmerie headquarters in the capital Niamey to the headquarters of the intelligence service, which is answerable to the presidency.