Journalists and conspiracy theories abound in Karachi

KARACHI (Reuters) - A huge billboard outside Pakistan's naval air force headquarters, which came under sustained attack for hours on Monday, says it all -- "Pakistan Air Force Museum. Unique experience."

Attacks against Pakistan security forces are all too common, but the scale of Monday's operation marked it out as the most audacious since the killing of al Qaeda leader Osama bin Laden by U.S. forces early this month.

Blasts rang out and helicopters hovered above the PNS Mehran base in the commercial hub of Karachi, for hours after more than 20 Pakistani Taliban militants stormed the building with guns and grenades on Sunday night, blowing up at least one aircraft.

The Pakistan Taliban, which is allied with al Qaeda, said the attack was to avenge bin Laden's killing. At least 12 military personnel were killed and 14 wounded.

It was not clear how many of the militants were killed.

"If these people can just enter a military base like this, then how can any Pakistani feel safe?" asked Mazhar Iqbal, 28, engineering company administrator taking a lunch break in the shade outside the complex where a crowd had gathered on a patch of grass to watch journalists set up camp as much as anything.

He said he was from an insecure area of the southern city already infamous as a source of funding for militant groups.

"The government and the army are just corrupt. We need new leaders with a vision for Pakistan."

Karachi has a population of about 18 million people, a volatile mix of rival ethnic groups and political factions, who all to readily resort to violence to settle scores.

Sprawling along the sun-baked coast of the Arabian Sea, the city is also home to Pakistan's main port, financial markets and the central bank.

It is also a transit point for military and other supplies to Afghanistan for the U.S.- and NATO-led anti-insurgency effort there.

QUESTIONS

The navy base is ringed with a concrete wall with about five feet of barbed wire on top. An aircraft, armed with rockets, hangs on show on a stand outside.

Two white paramilitary ranger vehicles had taken up position outside the main gate, each with a machinegun on top and an officer wearing a black cap and camouflage.

There were about 30 to 40 journalists gathering outside, with seven satellite dishes attached to their trucks. Helicopters buzzed overhead and the main road outside was closed to traffic.

Moin Babar, 35, a technical engineer, said people were trying to understand how the militants made it inside.

"I heard that 15 went in through a sewer," he said.

Kamran Khalil, 48, a civil engineer, suggested, like many others, a conspiracy.

"How can this happen? It's taking them so long to resolve the issue. India or the CIA could have been behind this. They want to show that Pakistan forces are ineffective."

Many in Pakistan were furious with the U.S. operation to kill bin Laden without sharing any intelligence beforehand with Islamabad, which they saw as a severe breach of sovereignty.

"This is all a reaction to American policy in Pakistan," said Atif Ali, a 30-year-old construction worker, standing near one billboard advertising audio equipment in which a beautiful woman says "Let's play" and another advertising pizza.

(Writing by Nick Macfie; Editing by Robert Birsel)