At least 10 people have been killed and 30 injured in a bomb explosion at a market in the Pakistani city of Quetta, officials say.
Police in Quetta said the bomb was attached to a cycle
Reports said that the bomb exploded near an army truck in the city, the capital of Balochistan province.
A little known group, the Balochistan Liberation Army, says it carried out the attack.
The group is fighting against what is sees as the dominating influence of Punjabis on political life.
The Balochistan Liberation Army spokesman, Azad Baluch, told the BBC it had targeted the military truck "to express our anger".
He expressed regret for the civilian casualties.
The group has claimed responsibility for a number of other attacks this year.
Both soldiers and civilians were among the casualties, police said.
Pakistan's President Pervez Musharraf said the blast was carried out by those "working against peace and
development in the country".
Information Minister Sheikh Rashid Ahmed said: "The people responsible will not go unpunished."
The explosion occurred in the centre of a business district.
Bomb disposal officials said the bomb, which was attached to a bicycle, could have been up to 20kg in weight.
"Thank God it was Friday and the bazaar was closed," Quetta's mayor, Mohammed Rahim Kakar, told the BBC, "otherwise the death toll would have been very high."
Police are investigating whether the bomb was a timed device or remote-controlled.
Quetta police chief Parvez Rafee Bhati said the attack represented a change of tactics by militants.
"They are using bicycle bombs now as security measures taken by the authorities have made it impossible for them to fire rockets from the outskirts," he said.
Television pictures showed chaotic scenes as the injured were loaded into minibuses and ambulances.
At least four vehicles were destroyed and windows blown out in nearby buildings.
Vegetable seller, Ali Mohammad, told the AFP news agency: "Nobody knew what happened. We thought it was an earthquake. There were dead bodies and wounded and blood was splattered."
Security has deteriorated in Balochistan in the past 12 months.
The BBC's Aamer Ahmed Khan in Karachi says there have been more than 30 bomb attacks in Quetta, but none have been as deadly as Friday's blast.
Quetta has also experienced sectarian violence.
In March, more than 40 Shia Muslims died when Sunni Muslim gunmen fired on a procession.
Quetta has also been a centre of operations for Pakistani security forces tracking al-Qaeda members.
In September they arrested an alleged senior al-Qaeda operative, Sharif ul Misri.