The FBI has arrested an Islamic State supporter from Ohio who allegedly plotted to attack the US Capitol using a bomb and semi-automatic rifles.

Christopher Lee Cornell, a 22-year-old from the Cincinnati area, was charged with buying and possessing firearms and attempting to kill US government officers and employees.

According to documents filed in the US District Court for the Southern District of Ohio, Cornell claimed that by conducting an attack he would be "fulfilling the directives of violent jihadists".

Cornell caught the FBI's attention in autumn after posting a series of messages and videos on Twitter under the alias Raheel Mahrus Ubaydah, claiming to support Islamic State and making threats against members of Congress.

In a series of instant message conversations and two meetings with an FBI informant, he allegedly claimed that he was not in contact with the terrorist group in Iraq and Syria, but suggested they "should wage jihad under our own orders and plan attacks on everything".

Cornell allegedly said that members of Congress were his enemies and that he intended to attack the Capitol using bombs and firearms, reports the Washington Post.

According to court documents, Cornell told the informant he wanted to "move" in December and showed him information on how to make a pipe bomb.

Plans for an attack and instructions for pipe bombs were found on his computer, said the FBI.

It was when he bought two semi-automatic rifles and around 600 rounds of ammunition in Ohio and made final plans to travel to Washington that he was arrested.

Nevertheless, John A Barrios, acting special agent in charge of the FBI's Cincinnati division, said the public was not in danger during the investigation.

Cornell's father, John, insisted that his son would not have been capable of carrying out an attack, despite posting angry messages about violent jihad.

He told ABC News that his son was a recent convert to Islam and that he had never spoken about any kind of violence to his parents. "He is a mummy's boy," he said, "he tells mummy everything."