A plume of smoke rises after an explosion at the Mehran naval aviation base which was attacked by militants in Karachi May 22, 2011. – Reuters Photo

KARACHI: A police account released Tuesday on the brazen, 18-hour Taliban assault on a Pakistani naval base says there were twice as many attackers as the number claimed by the government and navy, adding to the questions surrounding the deadly incident.

The attack Sunday in Karachi humiliated Pakistan's powerful military establishment and raised concerns about extremist infiltration of security services as well as the safety of the country's nuclear warheads. The Pakistani Taliban said they staged the raid to avenge the May 2 killing of Osama bin Laden.

The militants destroyed two US-supplied surveillance aircraft and killed 10 people on the base.

On Monday, after commandos had retaken control of Naval Station Mehran, Interior Minister Rehman Malik said up to six assailants were involved, four of whom were killed and two of whom apparently fled. Although they had earlier estimated the number of militants at between 10 and 15, naval officials also revised their estimate to six attackers.

But police said Tuesday in the "first information report" that between 10 to 12 attackers were involved. Local police chief Shahrukh Khan said the report was written after consultation with a navy officer. Such a report is a formal part of opening an investigation into the attack.

A navy spokesman said he was looking into the discrepancy.

Many analysts were surprised that just six attackers could occupy part of the base for such a long time against a force of hundreds of commandos and navy marines. Pakistan security agencies are known to sometimes not give full accounts of terrorism incidents, and often hold suspects for months without informing the public.

The fact that the attackers managed to infiltrate so deep into the high-security base led to speculation they may have had inside information or assistance.