ISLAMABAD, Pakistan — The ability of only six armed extremists to storm a Pakistani navy base in the city of Karachi and hold out for 16 hours raised new fears Monday about the security of the country’s military installations, including its nuclear weapons sites.

The attack, which began late Sunday night and lasted into Monday afternoon, left 10 Pakistani security personnel dead. At least two U.S.-supplied planes were destroyed. Six Americans who were providing training at the site were rescued by Pakistani security forces while the shootout was going on.

It was an ignominious attack for Pakistan’s armed forces, coming three weeks after American helicopters flew deep into Pakistan undetected in a two-hour operation that resulted in the killing of al Qaida leader Osama bin Laden.

“This was a total failure of naval intelligence and the naval security system. They’ve apparently not recognized the fact that Pakistan is at war,” said Javed Hussain, a retired brigadier general who served in Pakistan’s elite commando force, the Special Service Group. “How is security at nuclear sites any different?”

Since mid-2007, Pakistani jihadists have turned on their own country, inspired by al Qaida. Most attacks have been suicide bombings, but Sunday's attack wasn't the first assault on a heavily guarded military installation. Squads of gun-toting extremists launched three similar attacks in 2009, including one on the country's military headquarters at Rawalpindi in a 24-hour siege that killed 14 soldiers and officers.

“Time and again these people have humiliated the armed forces," Hussain said. "We are underestimating the power of these terrorists to do physical as well as mental damage. The armed forces are no longer held in awe. People have starting feeling insecure.”

Interior Minister Rehman Malik said the attackers had used a blind spot between security cameras to enter the base unnoticed, suggesting that someone on the base had helped plan the attack.

A spokesman for the Pakistani Taliban said the attack was intended to avenge bin Laden's killing.

“It was revenge for the martyrdom of Osama bin Laden," said the spokesman, Ehsanullah Ehsan. "It was the proof that we are still united and powerful.”

Since bin Laden's death May 2, Pakistan's Taliban have launched three attacks that they say were retribution for the U.S. raid. The onslaught included a suicide bombing at a paramilitary training school in the northwest that claimed more than 80 lives and the bombing of a U.S. diplomatic motorcade in the city of Peshawar that claimed the life of one Pakistani passer-by.

Despite Taliban attacks that have killed an estimated 30,000 civilians and 5,000 soldiers since 2001, a wide range of Pakistanis blame the violence on the country’s alliance with the United States, and Pakistan's U.S.-backed government has done little to rally public opinion against the Islamist extremists. But Malik said the time had come for the nation to deliver a stronger message against the Taliban.

“There is no option; we have to face our enemies," he told a news conference. "There’s only one way, to say with one voice that al Qaida is our enemy, Taliban is our enemy.”

Malik, who toured the base Monday shortly after fighting ended at about 2 p.m., said the militants had entered the sprawling Mehran naval aviation base at about 10 p.m. Sunday by climbing over a wall.

He said the Taliban squad was made up of six attackers. The bodies of three had been found — he provided a cellphone photo that he'd taken of one of the dead — and a fourth was thought to be buried under rubble. Two are suspected of having escaped the scene, he said.

Among the Pakistani military dead were a navy lieutenant who headed the rapid response force at the base and was first at the scene, three firefighters, three navy commandos, a sailor and two paramilitary rangers.

The Taliban used rockets to destroy the two U.S.-supplied aircraft, Malik said. Eleven Chinese were rescued along with the American trainers, Malik said. China and Pakistan have close military relations.

The attack came a month after the chief of Pakistan's army, Gen. Ashfaq Parvez Kayani, had told a military graduation ceremony that the country had “broken the back” of the terrorists. Pakistan has one of the largest armies in the world, with around 600,000 personnel. It also has about 100 nuclear weapons, a stockpile that’s fast-growing, according to experts.

Ironically, that ceremony took place in Abbottabad, the town where bin Laden later was found, less than a mile from Pakistan's prestigious national military academy. (Shah is a McClatchy special correspondent.)

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