CINCINNATI - A 20-year-old man's Twitter posts sympathizing with Islamic terrorists led to an undercover FBI operation and the man's arrest on charges that he plotted to blow up the US Capitol and kill government officials.

Christopher Lee Cornell, also known as Raheel Mahrus Ubaydah, told an FBI informant they should "wage jihad," and showed his plans for bombing the Capitol and shooting people, according to a criminal complaint filed in federal court in Ohio Wednesday. The FBI said Cornell expressed his support for the Islamic State.

Cornell's arrest came only days after a grand jury indictment charged another Cincinnati-area resident with threatening to murder House of Representatives Speaker John Boehner.

Boehner spokesman Michael Steel said in a statement Wednesday: "Once again, the entire Congress owes a debt of gratitude to the FBI and all those who keep us safe."

The complaint against Cornell charges him with attempting to kill officers and employees of the United States.

Cornell was arrested Wednesday after buying two semi-automatic rifles and about 600 rounds of ammunition, authorities said.

The public was never in danger, said John Barrios, acting special agent in charge of the FBI's Cincinnati division.

A phone message and an email were left Wednesday for attorney Karen Savir, a federal public defender listed in court records as Cornell's attorney. A working phone number could not be found for Cornell's family.

The complaint alleges that an FBI informant began supplying agents with information about Cornell last year. The informant and Cornell, who lives in Green Township, first began communicating through Twitter in August 2014 and then through an instant messaging platform separate from Twitter, according to the complaint.

"I believe we should meet up and make our own group in alliance with the Islamic State here and plan operations ourselves," Cornell wrote in an instant message, according to the court document.

The two met in October in Cincinnati and again in November, the complaint states. Cornell told the informant at the November meeting that he considered the members of Congress as enemies and that he intended to conduct an attack on the Capitol, according to the complaint. The document says Cornell discussed his plan for them to travel to Washington and conduct reconnaissance of the security of government buildings including the Capitol before executing "a plan of attack."

Cornell planned for the two to detonate pipe bombs at and near the Capitol and then shoot and kill employees and officials, and Cornell had saved money to fund the attack, according to the complaint.

Cornell's father defended his son as a peace-loving person who endured incidents of abuse as a practicing Muslim.

John Cornell told The Cincinnati Enquirer that his son was a "momma's boy who never left the house."

On Tuesday, authorities had disclosed that Cincinnati-area bartender Michael R. Hoyt, who has a history of mental illness, had been charged with threatening to kill Boehner at a country club near his home with a gun or a poisoned drink. A grand jury indictment against Hoyt was filed in US District Court in Ohio on Jan. 7.

Hoyt has told authorities that he had been fired from the West Chester, Ohio, country club where Boehner was a member and "did not have time to put something in John Boehner's drink," according to court documents made available Tuesday. The documents also said Hoyt told authorities he was Jesus Christ and was going to kill Boehner because Boehner was mean to him at the country club and was responsible for Ebola.

Hoyt, 44, is being held for mental evaluation and treatment at a federal medical center.

Messages and emails left for an attorney listed for Hoyt have not been returned.