WASHINGTON (TIP): A US man was arrested on Wednesday for allegedly plotting an attack on Congress inspired by the ISIS jihadis, according to the Justice department and the FBI.

Christopher Cornell, 20, was taken into custody after he purchased two semi-automatic weapons and 600 rounds of ammunition in the US state of Ohio, according to a criminal complaint.

The Justice department said he was charged “with attempting to kill officers and employees of the United States” and possession of a firearm to carry out violent acts. According to the complaint, Cornell had opened a Twitter account under the pseudonym Raheel Mahrus Ubaydah, where his posts supported ISIS. The Washington Post said he does not appear to have any formal backing from overseas.

Rather, according to an affidavit in support of the criminal complaint, he indicated that by conducting an attack he would be “fulfilling the directives” of violent jihadis.

He is accused of sending messages to an informant from the FBI outlining his plans. “I believe that we should just wage jihad under our own orders and plan attacks and everything,” he told the informant, according to the complaint. He also said he planned to launch several attacks and wanted to target US officials in Washington.

In the fall of last year, an informant began cooperating with the FBI as a way to obtain favourable treatment in an unrelated criminal case and agreed to provide information about a person using the name Raheel Mahrus Ubaydah — Cornell’s alias on Twitter, the Post said.

“He considered the members of Congress as enemies and that he intended to conduct an attack on the US Capitol,” the complaint said.

According to the FBI document, he said he planned to “build, plant and detonate pipe bombs at and near the US Capitol, then use firearms to shoot and kill people.”

Cornell had been under surveillance since August 2014. This week, he allegedly made final plans to go to Washington and set off bombs. The arrest comes in the wake of deadly attacks in Paris last week. Chairman of the House Committee on Homeland Security applauded the FBI and said it was launching investigations the wider scourge of homegrown terrorism.