A Taliban spokesman claimed responsibility for the attack, one of the bloodiest yet in Pakistan's intensifying war with insurgent groups that are also destabilizing Afghanistan.
The bombers struck at two different gates just as workers were leaving the sprawling arms facility in Wah, a garrison city 20 miles west of the capital, Islamabad.
Rana Tanveer, who was working at a bank about 200 yards from one of the gates where a bomber struck, said he was among the first to reach the scene.
"All around the gate I saw blood and human flesh. People helped the injured and took them in their cars and even on motorbikes to the hospital," he told The Associated Press. "Seven or eight people were already dead and another 10 people were breathing their last."
Tanvir Lodhi, a spokesman for Pakistan Ordnance Factories, said 59 people were killed. Mohammed Azhar, a hospital official, said 70 others were wounded.
Among more than a dozen bodies seen by an AP Television News reporter at the hospital were two wearing uniforms, though an army spokesman said he had no information that security forces were among the dead.
Pakistani forces are involved in an escalating battle with Islamic extremists in two nearby regions of the country's violence-plagued northwest, despite government efforts to negotiate peace with extremist groups.
Last month, Pakistan's security services warned that a group of suicide bombers would fan out across the country in the coming weeks to target important locations. At least 11 militants were arrested then, including five who were trained suicide bombers, during a raid in Lahore, Pakistan's second largest city, says CBS News reporter Farhan Bokhari.
"There are many indications to suggest that more attacks are planned. Pakistan could face a lot of bloodshed as it tries to deal with a very difficult problem," said a Western diplomat in Islamabad who spoke to CBS News on condition of anonymity.
Maulvi Umar, a spokesman for Tehrik-e-Taliban Pakistan, a militant umbrella group, said the suicide bombings were revenge for airstrikes in Bajur, a militant stronghold near the Afghan border.
Umar said militants would carry out similar attacks in other major cities, including Islamabad and the southern port metropolis of Karachi, unless the military halts its operations.
"Only innocent people die when the Pakistan army carries out airstrikes in Bajur or Swat," he said, referring to a mountain valley where the army has vowed to clear out militants who have kidnapped and killed police and troops and burned girls' schools.
"If the army is really fond of fighting, it should send ground forces to see how we fight," Umar told AP by telephone from an undisclosed location.
Regional police Chief Nasir Durrani said the bomber struck as workers were streaming out after a shift change at the weapons complex, Pakistan's largest.
"There are two torn bodies lying there which we believe are those of the suicide bombers," Durrani said.
Soldiers and police later sealed off the area and prevented reporters from approaching. Television footage showed workers struggling to lift a blackened corpse onto a stretcher. Crows as well as forensic teams picked through the scraps of flesh and scattered shoes.
Durrani said experts would try to reconstruct the bombers' faces to try to identify them.
At the hospital, relatives searched frantically for loved ones as doctors worked to save those most seriously injured.
A young man who gave his name as Mohammad Asif stood wailing after identifying the lifeless body of his 60-year-old father in an ambulance.
"He was a humble man ... What wrong did he do to anyone? Why was he punished? These cruel people have taken away the great shadow of my father," Asif said.
The bombers managed to enter the cantonment area of the town undetected, but did not penetrate the tightly controlled weapons complex, which houses about a dozen factories.
According to the army, the factories produce rifles, machine guns and ammunition as well as grenades, and tank and artillery shells. Abbas said the perimeter is guarded by a dedicated paramilitary force.
Experts have suggested that facilities related to Pakistan's secretive nuclear weapons program are located in the Wah area, possibly including a uranium enrichment plant. Abbas insisted the complex attacked on Thursday was producing only conventional weapons.
Meanwhile, one of the government's main coalition partners threatened Thursday to quit unless judges fired by former President Pervez Musharraf are quickly reinstated - dashing hopes that Musharraf's departure would end the nation's turmoil.
The two main parties - traditional rivals united primarily in their hatred of Musharraf - also diverge on who should succeed him as president and whether the former strongman should face trial.
The coalition's biggest bloc, the Pakistan People's Party, already appears to be lining up smaller parties in parliament to keep control of the government if the party led by former Prime Minister Nawaz Sharif pulls out of the coalition.
"The future of this coalition is linked to the restoration of judges," Sharif's spokesman Sadiqul Farooq told The Associated Press. "If the judges are not restored, we will prefer to sit on opposition benches."