ISLAMABAD, Pakistan - At least one aircraft was destroyed and several security personnel were feared injured or killed when unknown militants launched ?attack on an airbase of Pakistan Air Force (PAF) in the country's northwest district of Attock early Thursday morning, said local media. ?

Four to six militants were also killed in the attack, said local TV channel ARY. However, the report about the casualties has not been confirmed by the army.

Army spokesman Colonel Atiq confirmed the attack, saying that at the request of PAF, army commandos have been sent to the site to reinforce the security forces fighting against the militants.

According to local media and army sources, the attack took place at about 2:00 am Thursday when a group of militants launched attack on a checkpost of the Kamra Airbase, some 70 kilometers northwest of the country's capital Islamabad.

The militants opened fire and hurled hand grenades at the post guards when they were stopped at a fourth checkpost of the airbase, said local media. The militants wearing military uniforms had successfully crossed over three checkposts before they launched the attack.

Eyewitnesses said that huge smoke and fire were seen rising from the airbase following the attack.

One militant's body recovered on the spot wore a suicide jacket, said local TV Geo.

Following the attack, all the roads leading to the airbase have been closed.

There are normally around 30 jet fighters in the Kamra Airbase, and there is also an ?assembly line which produces the country's most advanced JF-17 Thunder jet fighters, said local media.

No group has claimed responsibility for the attack yet.

On May 22, 2011, Pakistan Taliban launched attack on an airbase in the country's southern port city of Karachi, destroying at least one US-made P-3C Orion aircraft and killing a number of soldiers.