"Following a meticulous preliminary examination of the situation, I have come to the conclusion that all legal criteria required under the Rome Statute to commence an investigation have been met," Fatou Bensouda said in a statement on Friday.
The prosecutor did not name the specific parties she seeks to investigate. But in a report last year (pdf), ICC prosecutors said the Taliban and its affiliates, Afghan authorities and members of the US armed forces and CIA may have committed war crimes.
"In due course, I will file my request for judicial authorisation to open an investigation, submitting that there is a reasonable basis to believe that war crimes and crimes against humanity have been committed in connection with the armed conflict in Afghanistan," Bensouda said on Friday.
She added it is up to the judges of the court in The Hague to decide whether the criteria to authorise an investigation are fulfilled.
Bensouda said that if authorisation is given, her office will investigate "in an independent, impartial and objective way, crimes within the court's jurisdiction allegedly committed by any party to the armed conflict".
"Members of US armed forces appear to have subjected at least 61 detained persons to torture," the prosecutors' office said in that report, adding that CIA members also seemed to have tortured 27 detainees in secret detention facilities elsewhere, but not in Afghanistan.
The report said that incidents appeared to have taken place in 2003 and 2004.
The US state department at the time said the probe was not "warranted or appropriate".
The 2016 report also said there "is reasonable basis to believe that" crimes against humanity were committed by the Taliban and its affiliates.
It said there was a basis to believe "war crimes of torture and related ill-treatment" were carried out by Afghan government forces.
The US forces occupied parts of Afghanistan after the attacks on September 1, 2011, to track Taliban and al-Qaeda leaders who Washington blamed for the attack. The US forces ended their combat mission in 2014.
Founded in 2003, the ICC seeks to prosecute war crimes and crimes against humanity.