Investigators interrogated at least a dozen suspects in the twin suicide bombings at Pakistan’s largest arms and ammunition factory this week. Six more people died on Friday from their injuries.

The latest casualties raised the death toll to 70 in the two synchronised attacks at the gates of the Pakistan Ordnance Factories (POF) in the garrison town of Wah Cantonment, 30 kilometres north-west of Islamabad.

Three suspects were rounded up in the area shortly after the bombers blew themselves up among hundreds of POF workers as they left the sprawling complex on Thursday after a shift change.

Initial reports said two bombers struck outside the factory but Rehman Malik, the security adviser to Prime Minister Yousaf Raza Gilani, said there had been three bombers.

"The fourth bomber was arrested before he could strike," he was quoted as saying by the English-language DawnNews television channel.

A security official, who spoke on condition of anonymity, said the suspected bomber was detained at a mosque close to the site of the carnage and a suicide vest and explosives were also seized.

"It is not clear so far whether he was waiting to strike his target or had changed his mind," he added.

Investigators said the attackers had layered ball bearings and nails onto the explosives to maximize the impact, adding that the explosives were of the same type as those used in last year's strikes on military targets in the nearby city of Rawalpindi, where Pakistan's army has its headquarters.

Regional police chief Nasir Khan Durrani and a senior medical officer, Salahuddin, confirmed the death toll stood at 70.

"Still it can go higher as at least 25 of the victims are in a critical state," Salahuddin said.

An air of gloom settled over the garrison town as a mass funeral was held Friday morning.

Hundreds of people gathered on the lawns of Wah's central mosque as coffins were lined up amid a somber atmosphere.

"It's incomprehensible as to how the militants can justify such gruesome acts," said Abdul Majeed, a middle-aged man who lost one of his relatives in the bombings.

Maulvi Omar, a spokesman for the Pakistani Taliban, claimed responsibility for the attacks on Thursday, saying these were carried out to avenge the ongoing military operation in Bajaur and Swat districts.

Omar warned the government that more attacks will be carried out in major cities if the military operations were not called off.

Pakistan Air Force units have been attacking militants in Bajaur tribal district bordering Afghanistan since the beginning of August.

Hundreds of militants have been killed in the fighting, while around 250,000 people fled from the conflict zone after the authorities gave calls for evacuation to avoid collateral damage.

Security adviser Malik said Thursday the government now had only two options - either to surrender to the militants or to take them on.

"The Pakistani nation must come forward against the militants and the extremists," Malik said, as the Interior Ministry received intelligence reports that at least six suicide bombers had entered key towns to carry out attacks.