Rescue workers gather at the site where a plane carrying Guinea's military chief, General Kelefa Diallo, and other senior military officials from the West African state crashed in Charlesville, some 40 km (25 miles) southeast of Monrovia, February 11, 2013. [Agencies]

MONROVIA/CONAKRY - 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.

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 military, which seized power in the former French colony in 2008. Some 4,000 soldiers were forced to retire under a UN-backed scheme to slim the 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.