ISLAMABAD, Pakistan -- Militants attacked an air force base in northwest Pakistan filled with F-16s and other aircraft before dawn Thursday, sparking a heavy battle with security forces that left parts of the base in flames, officials said.

The attack on the base in Kamra, located only about 85 kilometres (50 miles) northwest of Islamabad, was a brazen reminder of the threat posed by Islamist militants in Pakistan despite numerous military offensives against their sanctuaries along the Afghan border.

The militants infiltrated the base under the cover of darkness and began battling security forces at around 2 a.m., said Hafeez Aulakh, a police officer standing outside the base. The fighting was still going on three hours later, he said.

"We are outside the base and we are just hearing gunshots and sometimes small blasts," Aulakh told The Associated Press by telephone.

Special forces soldiers who joined the group trying to retake the base found the body of a suicide bomber inside, said the Pakistani air force, adding that the bomber was strapped with explosives. The air force said the battle's intensity had fallen from its height.

There were no immediate reports of casualties.

No group has claimed responsibility for the attack, but suspicion will likely fall on the Pakistani Taliban, who have waged a bloody insurgency against the government for the past several years that has killed tens of thousands of people.

While the group has carried out hundreds of bombings and other attacks through the country, raids against military bases are somewhat uncommon.

Half a dozen Taliban militants attacked a major naval base in the southern port city of Karachi in May 2011, killing at least 10 people and destroying two U.S.-supplied surveillance aircraft. It took Pakistani commandos 18 hours to retake Naval Station Mehran, and two of the attackers managed to escape. That the attackers managed to infiltrate so deep into the high-security base led to speculation they may have has inside information of assistance.

There have been at least three attacks in the vicinity of the Kamra air force base in recent years, but all of them occurred outside the installation.