ISLAMABAD: Pakistan's intelligence services warned the government three months ago about a possible attack on a prison in the restive northwest that was raided at the weekend, officials said Tuesday.

On Sunday nearly 400 prisoners, including militants, escaped from a jail outside the town of Bannu after an attack by insurgents armed with guns, grenades and rockets.

The intelligence information was conveyed to the government through a letter dated January 5, 2012, a copy of which was seen by AFP.

The letter identified Bannu jail as a target, along with the Pakistan Air Force base in the northwestern garrison town of Kohat, the Kohat cantonment and a police station.

“The intelligence information about the possible attacks was shared with the government in January 2012,” a senior intelligence official told AFP on condition of anonymity.

More than 150 heavily-armed militants stormed the prison where Taliban and al Qaeda linked militants have carved out their stronghold.

Ehsanullah Ehsan, spokesman for the Tehreek-e-Taliban Pakistan (TTP) militant group claimed responsibility for the attack, which he said was launched to free some of their top members.

A former member of the air force sentenced to death for an attempt to assassinate former president Pervez Musharraf was among the escaped militants, he said.

Adnan Rasheed was convicted after a bomb planted under a bridge in Rawalpindi near Islamabad in December 2003 exploded moments after Musharraf's motorcade passed. His appeal is pending before the Supreme Court.

The intelligence official said Rasheed was the only high-profile militant in the jail and the attackers were heard shouting his name after breaking in.

He said the government had also been warned of future attacks which would not be confined to the troubled northwest Khyber Pakhtunkhwa province.

Another intelligence official said: “Intelligence agencies had intercepted that an attack on Bannu jail to free inmates was being planned. But the date and time of the attack was not known.”

He also said Kohat air base, cantonment and Bannu jail had been identified as targets and that law enforcement agencies had been informed.