There is a "reasonable basis" to believe that US forces may have carried out war crimes, including torture, in Afghanistan, prosecutors at the International Criminal Court said Monday.

US armed forces "appear to have subjected at least 61 detained persons to torture, cruel treatment, outrages upon personal dignity," ICC chief prosecutor Fatou Bensouda said in her initial report.

The report also said a further 27 people were tortured by the CIA, with the majority of the alleged crimes said to have taken place between 2003 and 2004.

The US never ratified the ICC's founding treaty but as the alleged abuses were committed in Afghanistan, as well as Poland, Lithuania and Romania, which are all parties, the court has jurisdiction.

Monday's report claimed the crimes were not isolated, but were part of "approved interrogation techniques in an attempt to extract "actionable intelligence" from detainees."

"There is a reasonable basis to believe these alleged crimes were committed in futherance of a policy ... aimed at eliciting information through the use of interrogation techniques involving cruel or violent methods which would support US objectives in the conflict in Afghanistan," it said.

The court, which was established in 2002 to prosecute war crimes, crimes against humanity and genocide, said it would decide "imminently" whether to commence a full investigation.

In November, then Republican candidate Donald Trump said he would to reinstate waterboarding - a torture method which simulates drowning - and techniques that were "a hell of a lot worse" to obtain information from terrorists.

"Would I approve waterboarding? You bet your ass I would. In a heartbeat. I would approve more than that. It works," he told supporters at a campaign rally.