A 15-year-old boy has been arrested for allegedly threatening to launch an attack on Pope Francis inspired by ISIS, according to ABC News.

The Philadelphia teen planned to attack the Pope during his tour of the United States next week and was arrested quietly last month.

The boy had been radicalised by ISIS through social media, a tool that has been used effectively by ISIS in the US on many occasions.

"The minor was inspired by [ISIS] and sought to conduct a detailed homeland attack which included multiple attackers, firearms, and multiple explosives, targeting a foreign dignitary at a high-profile event," according to the FBI and Department of Homeland Security bulletin.

According to ABC, the "foreign dignitary" referred to is the Pope, who is visiting Philadelphia later this month.

The boy had explosives instructions and planned to share them through social media.

He has been charged with attempting to provide material support to a terrorist organisation and attempting to provide material support to terrorist activity, according to the bulletin.

The boy's plans were more "aspirational" than posing a real threat.

It has become clear that ISIS' use of social media is effective in radicalising young Americans.

This, among other cases, "demonstrates that some youth are vulnerable to messaging from [ISIS] supporters."

Their "innovative use of social media and messaging has played a key role in motivating young US based males and females to travel to join the self-declared Islamic State or allegedly attempt to conduct attacks in the Homeland on behalf of" ISIS, according to the FBI-DHS intelligence bulletin.

"These incidents also show that some US-based youth are willing to connect over social media with like-minded persons, and have proven adept at obfuscating such social media usage from their parents and guardians."