A huge explosion at Beagram airbase in Afghanistan, the largest US military facility in the country, has killed at least four people.
At least 14 others were wounded in the blast. The Taliban said one of their suicide bombers carried out the attack.
The attack is being seen as a major security breach in one of the best protected places in Afghanistan.
The bomb reportedly exploded inside the base, which if confirmed, would be the first attack of its kind.
Attacks on Bagram have occurred in the past but insurgents have never made it past the compound’s outer walls.
Bagram, just north of the capital Kabul, has been used as the main military base and airfield by the US-led forces and Nato over the past 14 years.
A local government spokesman, Abdul Wahid Sediqi was quoted as saying the attacker entered the base early in the morning on foot hidden among a group of workers reporting for duty.
“We don’t know the identity of victims yet but the attacker was one of the Afghan labourers working there,” Abdul Wahid Sediqi said.
Bagram is a heavily guarded military base with many layers of security and protection.
The outermost layer is guarded by Afghan forces and second and more inner layers of security are guarded by US forces.
High walls, security cameras and watch towers on the outer perimeters and inside the base are just some of its formidable security measures. A surveillance balloon also watches the entire area.
Every person entering the base is searched, in many cases escorted and must have a pre-arranged meeting with someone inside.
The security measures serve not only to protect military personnel on the base, but also to safeguard expensive state of the art military tools, including fighter jets and unmanned aerial technology.
US presidents visiting the country fly into Bagram, one of the most heavily guarded places in Afghanistan, because it is seen as more secure than landing in Kabul.
US Army commander in Afghanistan, General John W Nicholson said in a statement: ”[To] the family and friends of those wounded in today’s attack, let me assure you they are receiving the best care possible, and we will keep them in our thoughts today.”
He said the incident was being investigated but did not disclose the nationalities of the casualties.
Taliban spokesman, Zabihullah Mujahid said the blast had inflicted “heavy casualties on US invaders.”
Last December, a Taliban suicide bomber riding a motorbike killed six US soldiers in a village near Bagram in one of last year’s deadliest attack on foreign troops.
The attack on Bagram comes just a day after the German consulate in the city of Mazar-e-Sharif in northern Afghanistan was hit by a Taliban suicide bomb blast that killed six civilians and wounded some 120 others.
The Taliban said on Friday the attacks were carried out in retaliation for a recent coalition airstrike in Kunduz which reportedly killed some 30 civilians.