* Crash killed six officials and five crew - Guinea government
* General Kelefa Diallo was close ally of President Alpha Conde
* Diallo was architect of reforms of Guinea's restive military (Adds discovery of flight recorder)
By Alphonso Toweh and Saliou Samb
MONROVIA/CONAKRY, Feb 11 (Reuters) - The head of Guinea's armed forces, a staunch ally of President Alpha Conde, was killed on Monday when the aircraft carrying him and five other top Guinean military officials crashed close to the Liberian capital Monrovia.
General Souleymane Kelefa Diallo, who was on a security mission to Liberia, was appointed by Conde after the latter won elections in 2010 in the world's top bauxite producer.
Diallo was charged with reforming the restive army in the West African state after two years of military rule.
Investigators and United Nations peacekeepers picked through the charred wreckage of the aircraft amid a grove of palm trees near Charlesville, some 40 km (25 miles) southeast of the Liberian capital Monrovia. There were no survivors.
"This accident cost the life of six members of the delegation, including General Souleymane Kelefa Diallo, head of the armed forces, and five members of the crew," Guinea's Defence Minister Abdoul Kabele Camara said in a statement.
Liberian President Ellen Johnson-Sirleaf, who visited the crash site in the company of Guinea's ambassador to Liberia, declared a national day of mourning for Tuesday.
Liberia's Defence Minister Brownie Samukai said the cause of the crash was not immediately clear. Rescue crews retrieved the plane's flight recorder - its so-called black box - from the wreckage, however, and Liberian authorities said they planned to send it to Canada for analysis.
General Diallo was one of the main architects of the reform of Guinea's powerful military, which seized power in the former French colony in 2008. Some 4,000 soldiers were forced to retire under a U.N.-backed scheme to slim the bloated armed forces.
Diallo's predecessor, Nouhou Thiam, is in prison facing trial for his alleged role in a gun and rocket attack on President Conde's home by soldiers in 2011.
Conde's government has been trying to organise legislative elections for May, the final step in the transition back to civilian rule and a prerequisite to unlock millions of dollars of frozen foreign aid.
The opposition, alleging bias in the electoral authority, has called protests for Wednesday this week. Conde's 2010 election in a vote hailed as the first free elections since the end of French rule in 1960 was marred by deadly riots and opposition allegations of fraud. (Writing by Daniel Flynn; Editing by Pascal Fletcher and Michael Roddy)