* Diplomats say promotion to push Sanogo towards retirement
* Mali elected new president on Sunday
* Seeking clean slate to reform army after coup (Adds diplomat comment)
By Tiemoko Diallo
BAMAKO, Aug 14 (Reuters) - Mali's outgoing government has promoted to the rank of general an army captain who led a coup last year that plunged the West African nation into crisis and allowed al Qaeda-linked fighters to seize the desert north.
Diplomats in Bamako said the surprise move by the government of interim President Dioncounda Traore was meant to push Captain Amadou Aya Sanogo towards retirement to allow president-elect Ibrahim Boubacar Keita to start with a clean slate.
The decision, which was criticised by rights groups, comes just days after Mali held the election to draw a line under more than a year of political turmoil and war.
"I confirm that Captain Sanogo was proclaimed a four-star general ... (The nomination) was signed this morning by the president of the republic," spokesman Captain Modibo Naman Traore said on Wednesday.
Sonogo has maintained influence despite officially handing power back to civilian leadership last year.
Diplomats said he had resisted pressure to leave the army until he received the promotion to four-star general, which gives him the status of a former head of state and immunity from prosecution.
"This was a move taken for the sake of stability," said one Western diplomatic source. "They want him out of the army as quickly as possible."
Malian authorities are keen to ensure other members of the former military junta retire as the country presses ahead with a reform of its armed forces under the aegis of a 560-strong EU military training mission.
Colonel Moussa Sinko Coulibaly, another former junta member who serves as minister of territorial administration in Mali's interim government, was promoted to brigadier general.
The decision to promote Sanogo outraged Human Rights Watch which, along with other campaigners, accused the junta of arbitrary detention, torture and enforced disappearances.
"Instead of being rewarded for his behaviour, Sanogo should have been investigated for his involvement in very serious abuses committed over the last 18 months," said Corinne Dufka, who investigated the abuses for HRW.
Once portrayed as a model democracy, Mali imploded when the junta, frustrated by a lack of progress in tackling a Tuareg rebellion in the north, toppled President Amadou Toumani Toure in March 2012.
The Tuareg rebels and their Islamist allies seized upon the turmoil in the capital Bamako to launch a rapid advance, capturing two-thirds of the country.
The al Qaeda-linked fighters were finally defeated following the intervention of thousands of French soldiers in January.
Malians elected former prime minister Keita in a presidential runoff on Sunday. He is due to be inaugurated on Sept. 19. (Additional reporting by Dan Flynn; Writing by Joe Bavier; Editing by Alison Williams)