The device strapped to a bicycle on Friday tore through a crowded market in the city, the capital of poverty-stricken Baluchistan province, killing passersby, vendors and a soldier.
The Baluchistan Liberation Army, a self-proclaimed nationalist group, said it carried out the attack. "Our target was the military truck," said Azad Baluch, calling himself the group's spokesman.
"It was to express our anger," he said in a telephone call from an unknown location to journalists at Quetta Press Club.
The province is in the throes of a low-level tribal uprising fuelled by resentment that foreign investors and richer neighbouring provinces are creaming off profits from the region.
The bomb blast took place at an
area frequented by soldiers
Some tribal leaders have opposed a government plan to establish at least three garrisons in the region, which is rich in natural resources.
The blast happened at about 4pm (1100 GMT) when the market in the centre of Quetta, the capital of Baluchistan province, is usually crammed with people.
Military spokesman Major-General Shaukat Sultan described the blast as a "terrorist act" and Information Minister Shaikh Rashid blamed the attack on "enemies of the country".
He told state television: "The culprits of such heinous crimes are terrorists. They do not want to see development of the country."
Dirt-poor Baluchistan has been
wracked by all kinds of trouble
Police said the device exploded in Quetta's main Mizaan Chowk commercial district near a military vehicle carrying soldiers visiting the area for weekly shopping.
The truck, which belongs to the Staff College, was badly damaged, along with three private cars. Television footage showed scenes of chaos, with agitated crowds loading injured people into minibuses and ambulances.
"Nobody knew what happened. We thought it was an earthquake," vegetable seller Ali Muhammad, who was sitting across the road, said.
"There were dead bodies and the wounded. Blood was splattered in the area," he said.
State of emergency
Nasir Khan, a medical officer at Quetta's Civil hospital, said they had received seven bodies and two seriously wounded people died later. "One of the dead is a soldier," he added.
The hospital declared a state of emergency.
"Nobody knew what happened. We thought it was an earthquake"
Vegetable seller Ali Muhammad
The injured included five soldiers who were being transferred to a military hospital, Khan added. In total, about a dozen people suffered serious injuries, including one of the soldiers.
Akbar Ali, director of the local bomb-disposal unit, said: "We are investigating if it was timed device or a remote-controlled bomb."
In November, a bicycle bomb thought to be aimed at a vehicle of the paramilitary Frontier Corps killed one man and injured 15 people, including a soldier in Khuzdar, 250km south of Quetta.
It came a day after a bomb exploded near a police station in Quetta, injuring three passersby.