The officers were on their way to attend Liberia's Armed Forces Day celebrations Monday morning when the plane crashed in Charlesville, near the country's largest airport and about 45 kilometers (28 miles) south of the capital, Monrovia. It exploded moments later, witnesses told news agencies.

Liberian Defense Minister Brownie Sakal said the cause of the crash was not immediately clear, investigators were dispatched to the site along with rescue workers and UN peacekeepers.

"I have the profound regret of informing the people of Guinea of the tragic military plane accident that happened this Monday, Feb. 11, 2013, around 7:30 a.m. in Liberia," Guinean President Alpha Conde said in a statement released by the Defense Ministry. "This accident cut short the lives of six members of the delegation led by General Souleymane Kelefa Diallo."

On Monday afternoon Liberian President Ellen Johnson Sirleaf visited the crash site, just 5 kilometers from the airport. Earlier in the day, Sirleaf had called for a moment of silence and declared Tuesday a day of mourning. Guinea has called for a three-day grief period.

Diallo had worked to reform Guinea's military, which seized power in 2008. About 4,000 soldiers were forced to retire under a UN-backed scheme to slim the bloated armed forces. Diallo's predecessor is in prison, awaiting trial for his alleged role in a gun and rocket attack on President Conde's home by soldiers in 2011.

General Namory Traore has been appointed interim army chief of staff, according to Conde's statement.

mkg/msh (Reuters, AFP, dpa, AP)