Mr Moreno Ocampo, a lawyer from Argentina who helped lead the 1985 prosecution of that country's former military junta, described the strikes as a "very dangerous" expansion of the president's remit to use lethal force. In the past, he said, alleged drug boats would be stopped and suspects incarcerated.
"The US is alleging it can kill whoever they want, and that's a huge change because in the past the US, in particular after 1945, was the guarantor of global peace to protect Western values, basically," he said.
"That's… a very bad trend for the world," added Mr Moreno Ocampo, who served as the first chief prosecutor at the ICC from 2003 to 2012, opening investigations in seven different countries.
The US is not a signatory to the Rome Statute which established the ICC and has recently sanctioned several of its judges in retaliation for the court's investigations related to the US and Israel.
Mr Moreno Ocampo said: "For me, it's very clear. A crime against humanity is a systematic attack against a civilian population, and there is no clarity why these people are not civilians, even [though] they could be criminals... and it's clearly systematic, because President Trump says they have planned and they organised this, so that should be the charge."