Some of those who escaped from the jail in the town of Bannu were militants, an intelligence official said. A police official said that of a total 944 prisoners in the jail, 384 had escaped.
One of the escaped prisoners was believed to be on death row for involvement in an assassination attempt on the former Pakistani president Pervez Musharraf. "There was an inmate named Adnan Rasheed, who was a dangerous prisoner. He was a mastermind in [one of the attacks] on Musharraf. These people came for him and took another 383 people too," the police official said.
Pakistan's Taliban movement, which has close links to al-Qaida, said its fighters had mounted the assault, which triggered clashes.
"We have freed hundreds of our comrades in Bannu in this attack. Several of our people have reached their destinations, others are on their way," said a Taliban spokesman.
The claim could not be immediately verified. If the Taliban did free the prisoners, it could deal a psychological blow to Pakistani security forces, which say they have made gains against militants after a series of attacks on their strongholds. Police and intelligence officials said only some of the prisoners who escaped were militants.
"Dozens of militants attacked Bannu's central jail in the early hours of the morning, and over 300 prisoners have escaped," a senior police official, Mir Sahib Jan, told Reuters.
"There was intense gunfire, and rocket-propelled grenades were also used."
The Tehrik-e-Taliban Pakistan, or Taliban Movement of Pakistan, has carried out a campaign of suicide attacks and shootings in its drive to topple the US-backed Islamabad government.
