A US Afghanistan war veteran has been charged over an alleged plot to detonate a nail bomb at an LA white nationalist rally following an FBI sting on Monday.

26-year old Mark Steven Domingo is a former US Army infantryman who later converted to Islam. He was taken into custody on Friday after repeatedly stating he wanted to cause mass casualties.

Domingo engaged in internet conversations with an undercover FBI source, revealing his willingness to become a "martyr", and referencing the 2013 Boston Marathon bombing and 2017 shootings at a Las Vegas country music concert.