More than 30 people were also injured by the blast inside the high security zone of Colombo's main military base, police said.
The attack on Lieutenant General Sarath Fonseka's convoy was another blow to the island's troubled peace process and a bload-soaked truce.
Fonseka was riding in a silver Peugeot 406 which had three gold stars marked on a red background indicating it was his vehicle.
He was escorted by Land Rover Defender jeeps packed with armed soldiers and heavily armed motorcycle outriders, one of whom kicked the woman bomber as she tried to get near the convoy, a military official said.
"Five of his bodyguards who escorted the car on motorcycles were killed on the spot," a police official said.
"The commander was critically wounded," police chief Chandra Fernando told AFP. "The attack was well within the army headquarters.
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Doctors at the main National Hospital said 10 people were killed, but defence ministry spokesman Prasad Samarasinghe said he could confirm only eig