Militants armed with guns and rocket launchers stormed a key Pakistani air force base before dawn on Thursday, sparking heavy clashes with security forces, officials said.
Two Pakistani security officials were killed when six militants stormed an air force base northwest of the capital Islamabad on Thursday, a military spokesman told AFP.
All six attackers also died, a spokesman for the air force said, after the assault sparked a fierce firefight.
The attack began after 2:00 am (2100 GMT Wednesday) and fighting was continuing three hours later, but it was unclear how many assailants had penetrated PAF Base Minhas, in Kamra about 60 kilometres (37 miles) northwest of Islamabad.
One official speaking to AFP on condition of anonymity from within the base said he could hear gun and rocket fire, and the sound of hand grenades.
Officials said special forces were scrambled to respond to the attack at the base, home to the Pakistan Aeronautical Complex, the manufacturing division of the air force that builds Mirage and, with Chinese support, JF-17 fighter jets.
A Pakistan Air Force (PAF) spokesman said, "One body of a suicide bomber strapped with explosives has been found close to the impact area," he said, adding that the intensity of the clashes was lessening.
The Air Force had earlier confirmed that "a group of terrorists" had attacked part of PAF Base Minhas and that "intense fire is being exchanged between the security personnel".
There was no immediate claim of responsibility but Islamist militants linked to the Pakistani Taliban have targeted a string of military bases in a five-year insurgency.
In May 2011, it took security forces 17 hours to quell a similar attack on an air base in the southern city of Karachi that killed 10 security personnel and destroyed two US-made aircraft, and was claimed by the Taliban.
Despite a relative lull in high-profile attacks, Pakistan has been on alert for violence to coincide with its independence day on Tuesday this week and the Muslim festival of Eid, which is expected to begin at the weekend.
The government says 35,000 people, including more than 3,000 soldiers, have been killed as a result of terrorism that has swept the country since the 9/11 attacks in 2001 and the subsequent US-led invasion of neighbouring Afghanistan.
Pakistan has been fighting for years against homegrown Taliban in its northwestern tribal frontier with Afghanistan. But it has so far resisted US pressure to take on militants who use Pakistani soil to plan attacks across the border.
The military has been targeted at least twice in recent years in Kamra, in the central province of Punjab.
On October 23, 2009 a suicide bomber killed six civilians and two Pakistan Air Force personnel at a checkpoint outside the base during morning rush hour.
On December 10, 2007, a suicide car bomber struck a school bus, wounding at least five children of base employees.