29 July 2013 Last updated at 18:31 ET
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Taliban militants wearing police uniform have launched an assault on a prison in north-west Pakistan.
The attack on the jail in the town of Dera Ismail Khan began with several explosions at around midnight on Monday.
Gunmen then opened fire with rocket-propelled grenades and machine-guns, police chief Sohail Khalid said.
The prison houses hundreds of Taliban and militants from banned groups. The fighting is still going on.
The attackers were chanting "God is great" and "Long live the Taliban," officials told the Associated Press.
A local resident told the agency that the initial blast was so loud that "it rattled every house in the neighbourhood".
Pakistani Taliban spokesman Shahidullah Shahid has claimed responsibility for the attack. He said around 300 prisoners had been freed.
"The Taliban have loudspeakers and they are calling the names of their friends," the town's civil commissioner, Mushtaq Jadoon, said.
Officials said that authorities had been aware of a threat to attack the prison in recent weeks.
Provincial prisons chief Khalid Abbas said he was not sure if any of the jail's 40 "high-profile" prisoners had escaped.
Hundreds of inmates were freed in an assault on a prison in Bannu in northern Pakistan in April last year.
Dera Ismail Khan is the main city in Khyber-Pakhtunkhwa Province, in Pakistan's restive, mountainous tribal region.
Monday night's violence comes hours before Pakistani politicians are expected to choose the country's new president.
The replacement for Asif Ali Zardari will be elected on Tuesday by the members of both houses of parliament and the four provincial assemblies.
Continue reading the main story
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Taliban militants wearing police uniform have launched an assault on a prison in north-west Pakistan.
The attack on the jail in the town of Dera Ismail Khan began with several explosions at around midnight on Monday.
Gunmen then opened fire with rocket-propelled grenades and machine-guns, police chief Sohail Khalid said.
The prison houses hundreds of Taliban and militants from banned groups. The fighting is still going on.
The attackers were chanting "God is great" and "Long live the Taliban," officials told the Associated Press.
A local resident told the agency that the initial blast was so loud that "it rattled every house in the neighbourhood".
Pakistani Taliban spokesman Shahidullah Shahid has claimed responsibility for the attack. He said around 300 prisoners had been freed.
"The Taliban have loudspeakers and they are calling the names of their friends," the town's civil commissioner, Mushtaq Jadoon, said.
Officials said that authorities had been aware of a threat to attack the prison in recent weeks.
Provincial prisons chief Khalid Abbas said he was not sure if any of the jail's 40 "high-profile" prisoners had escaped.
Hundreds of inmates were freed in an assault on a prison in Bannu in northern Pakistan in April last year.
Dera Ismail Khan is the main city in Khyber-Pakhtunkhwa Province, in Pakistan's restive, mountainous tribal region.
Monday night's violence comes hours before Pakistani politicians are expected to choose the country's new president.
The replacement for Asif Ali Zardari will be elected on Tuesday by the members of both houses of parliament and the four provincial assemblies.