United States FBI has arrested an Ohio man on Wednesday (14 January) for allegedly trying to plot an Islamic State (Isis)-inspired attack on the US Capitol.

Authorities charged Christopher Lee Cornell, 20, for attempting to murder a US government official and planning to detonate pipe bombs at the US Capitol.

Cornell came under investigation several months ago after actively advocating for violent "jihad" on Twitter under the username 'Raheel Mahrus Ubaydah'.

Cornell allegedly posted content, including videos and statements, expressing his support for IS, according to government documents.

In one such message, Cornell writes to an FBI informant: "I believe that we should just wage jihad under our own orders and plan attacks and everything.

"I believe we should meet up and make our own group in alliance with the Islamic State here and plan operations ourselves."

The FBI informant and Cornell met in Cincinnati in October and November last year, and Cornell allegedly told the informant that members of the US Congress were his enemies and he is planning to launch an attack on the US Capitol in Washington, reported ABC News.

The FBI said what followed was extensive research on how to build bombs and Cornell saved funds to carry out the planned attack.

Cornell allegedly bought two semi-automatic rifles and 600 rounds of ammunition from a store in Ohio earlier today (14 January), authorities said.

The FBI and Department of Homeland Security released a statement to all law enforcement agencies in the US saying:

"The alleged activities of Cornell highlight the continued interest of US-based violent extremists to support designated foreign terrorist organizations overseas, such as ISIL [ISIS], by committing terrorist acts in the United States.

"Terrorist group members and supporters will almost certainly continue to use social media platforms to disseminate English language violent extremist messages."