United States President Joe Biden on Thursday vowed to punish the perpetrators of an attack outside Kabul international airport that killed 13 American soldiers and at least 72 Afghans.

Two explosions took place on Thursday evening as the US and other Western countries were completing the evacuation of tens of thousands of citizens and Afghans ahead of an August 31 deadline for the American troops to exit Afghanistan. Terror group ISIS-K (Islamic State of Khorasan) has claimed responsibility for the attack.

“We will not be deterred by terrorists,” Biden said in a speech from the White House. “We will not let them stop our mission. We will continue the evacuation. We will not forgive. We will not forget. We will hunt you down and make you pay.”

The president also bowed his head for a moment of silence for those who died in the attack before taking questions from journalists. During his speech, he also appeared occasionally close to tears and described those military members who died as “heroes who have been engaged in a dangerous, selfless mission to save the lives of others”.

Biden said he has ordered his commanders to develop operational plans against the assets, leadership and facilities of ISIS-K, which is an affiliate of the Islamic State. “We will respond with force and precision at our time, at the place we choose, and the moment of our choosing,” he added.

Responding to a question from a journalist, the US president said there was no evidence of any collusion between the Taliban and the ISIS-K in Thursday’s attack.

The 78-year-old Democrat said he would also deploy additional troops if required to protect American citizens in Afghanistan. He also reaffirmed that the US forces would fly out as many people as possible before the August 31 deadline.

The blasts on Thursday came hours after the US and allies of the North Atlantic Treaty Organization, commonly known as NATO, warned their citizens about the threat of an attack at the airport.