An explosion struck the largest US military base in early Saturday, causing some casualties, Nato said.
The Taliban claimed responsibility for the blast, which occurs as the group before the onset of winter, when fighting usually ebbs.
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“We can confirm that there was an explosion at Bagram Airfield this morning just after 5.30am (0100 GMT). There have been casualties,” the military coalition said in a brief statement.
“Our Force Protection and medical teams are responding to the situation,” it added, without offering any other details.
Abdul Shokor Qodosi, the district governor of Bagram, said that at least three people were killed and 13 injured in the blast, which he said occurred near a dining facility. The death toll was later lifted to four.
The nationalities of those killed were not immediately known after the blast.
“An explosive device was detonated on Bagram Airfield resulting in multiple casualties. Four people have died in the attack and approximately 14 have been wounded,” Nato said in a statement.
“Response teams at Bagram continue to treat the wounded and investigate the incident.”
Waheed Sediqi, spokesman for the governor of Parwan province where Bagram is located, said the blast was caused by a suicide attacker who blew himself up near a dining facility inside the base.
“We don’t know the identity of victims yet, but the attacker was either one of the Afghan labourers working there,” Sediqi told AFP.
Qodosi said the explosion that struck around 0100 GMT was powerful and reverberated across the area.
“To the family and friends of those who lost their lives today, we share your loss and our thoughts are with you. We offer you our deepest condolences,” said John Nicholson, the top US and NATO commander in Afghanistan.
“For 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.”
The explosion underscores a worsening security situation nearly two years after Nato formally ended its combat operations in Afghanistan.
Bagram Airfield, close to Kabul, has frequently come under attack by insurgents.
Last December, a motorcycle-riding Taliban suicide bomber killed six US soldiers near Afghanistan’s largest US military base.
It was one of the deadliest attacks on foreign troops in the country in 2015.