(CNN) Members of the military who followed a would-be President Donald Trump's order to kill terrorists' families could face a Nuremberg-like war crimes trial, a former U.S. defense secretary tells CNN.

There's "something called Nuremberg that we have to be concerned about," William Cohen told Christiane Amanpour, referring to the military tribunals held in the wake of World War II.

If "you have an order given by the commander in chief, which violates every sense of law and order, international law and order, that would make any of those who carried out that dictum as such to be a violation of the international criminal code."

"So I think we have to be very careful what we're saying here."

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Cohen served as a Republican senator from Maine for nearly 20 years, and as defense secretary during the second term of Bill Clinton's presidency.

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