LAHORE, Pakistan (CNN) -- A suicide bomber killed at least 23 people and injured more than 58 others after detonating an explosive outside a court in Lahore on Thursday, police said.
A rescuer helps an injured man following a suicide bomb attack in Lahore.
The exact number of casualties varied, but state-run news agency the Associated Press of Pakistan said 22 police officers and one passerby were killed.
Reports of another explosion triggered a dash toward a supposed second blast site, but those reports proved unfounded, said Aftab Cheema, senior superintendent of Lahore police.
The suicide blast occurred in the city's commercial district, moments before lawyers were set to begin a rally outside the high court in the eastern Pakistani city to protest the rule of President Pervez Musharraf.
No one immediately claimed responsibility for the attack.
Caretaker Prime Minister Mohammadmian Soomro said in a statement that those who committed this "cowardly act" were "neither believer of any religion nor of any human ethics."
Police said about 100 uniformed and plainclothes officers were at the scene ahead of the rally when the bomb went off about 11:45 a.m. Pakistan time (6:45 a.m. GMT).
The bomber was approaching a police barrier when officers stopped him, said Cheema, and the man then blew himself up.
Ahsan Bhoon, president of the Lahore High Court Bar Association, said lawyers had just completed a meeting and were headed out of the courthouse to participate in the rally when he heard the blast.
Bhoon said he saw bodies scattered everywhere. At least 15 of them were lifeless.
A second lawyer, Khurram Khosa, said he began picking up bodies of the dead and noticed all but one of them clad in the green uniform of police officers.
Many of the wounded were taken to Mayo Hospital in Lahore, said medical superintendent Fayyaz Ahmad Ranjha. Two remained in critical condition but the rest were likely to survive, Ranjha said.
Footage from the scene painted a chaotic picture, with baton-wielding police working to beat back a crowd that was trying to get a closer look at a burned-out white vehicle.
Officers cordoned off the area, while rescue workers carrying stretchers with wounded victims sidestepped shards of glass that littered the street from broken car windows.
"Lahore is typically a calm city," local journalist Todd Baer said. "This is one of the few places in Pakistan that did not have rioting (after the assassination of former Prime Minister Benazir Bhutto). So people here are very tense right now."
In recent months, Pakistan has been besieged by a wave of suicide attacks that has claimed several hundred lives.
The blast comes a day before the start of the month of Muharram, a holy period of mourning, when religious tension are high.
It also follows the death of Bhutto, who was killed at a rally in Rawalpindi, south of the Pakistani capital Islamabad, on December. 27.
While the cause of her death is still unclear, a bomber blew himself up near her limousine and videotape showed a gunman present.
Lawyers in Lahore have been holding rallies every Thursday to protest the government's crackdown on the judiciary and imprisonment of lawyers and judges across the country.
Meanwhile, Bhutto's Pakistan People's Party said it had written to the Pakistan government urging it to request an independent United Nations inquiry, The Associated Press reported on Thursday.
The PPP warned that if the government failed to do so within 48 hours, the party would approach the U.N. directly. E-mail to a friend
CNN's Mohsin Naqvi, Leone Lakhani, Ingrid Formanek and journalist Todd Baer contributed to this report.
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