At least nine people including three troops and six militants were killed in a terrorist attack on a Pakistan air force base in the country's southern port city of Karachi late Sunday night, local Urdu TV channel ARY reported.

Fire and smokes erupt from a Pakistan's military air base after an attack by militants in southern Pakistan's Karachi on May 23, 2011. [Xinhua]

Earlier news reports said that four foreigners were killed in the attack and they were believed to be U.S. engineers working at the air force base, but a spokesman for the U.S. embassy here denied the report, saying no U.S. nationals were killed in the attack.

The terror attack occurred at about 10:30 p.m. local time Sunday night when three explosions were first heard inside the air force base, followed by heavy gunfire.

The government troops immediately cordoned off the area shortly after the blasts, media people, even rescue teams and ambulances were not allowed to enter the area, no one knows what exactly is going on inside the air force base, said a witness.

Pakistani Interior Minister Rehman Malik later told a local media that a Pakistan air force base in Karachi is under terrorist attack.

Local media reports said that an estimated 10 to 15 terrorists were involved in the attack and they were armed with automatic weapons, rockets and handgrenades.

Up till now, nine explosions have been heard inside the air force base.

Pakistani Prime Minister Yousaf Raza Gillani has ordered Interior Minister Rehman Malik to watch over the situation. Navy forces, rangers and other armed forces have been dispatched to the air force base and helicopters are hovering over the air force base to monitor the situation there, according to local media reports.

News reports said that the terrorists are targeting at the airplanes dwelling in the hangars at the air force base. At least two airplanes have been destroyed completely and several others have caught fire during the gunfire.

Pakistan Taliban (TTP) has reportedly said they are responsible for the air force base attack.

Following the killing of al-Qaida chief Osama bin Laden by the U.S. special task force in Pakistan's northwestern city of Abbottabad early this month, both Pakistan Taliban and al-Qaida have vowed to avenge the death of bin Laden by threatening to launch attacks not only in Pakistan, but also in the United States as well as in the other parts of the world.

On May 13, Pakistan Taliban launched two suicide bomb attacks on an armed border police training center in the country's northwestern city of Charsadda, killing 98 people and injuring over 140 others. This is the first major attack launched by Pakistan Taliban following the killing of Osama bin Laden.