BBC News says it was said using a megaphone when talking to a large crowd:

Petro shared a video on social media of him addressing a large crowd through a megaphone in Spanish on Friday.

He called for the formation of a “world salvation army, whose first task is to liberate Palestine”.

“That is why, from here in New York, I ask all soldiers in the United States Army not to point their rifles at humanity,” he said. “Disobey Trump’s order! Obey the order of humanity!”