Washington - A US man was arrested on Wednesday for allegedly plotting an attack on Congress inspired by Islamic State jihadists, 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. Twitter accountAccording to the complaint, Cornell had opened a Twitter account under the pseudonym Raheel Mahrus Ubaydah, where he posted messages supporting Islamic State militants. He is accused of sending messages to an informant from the Federal Bureau of Investigations 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. "He considered the members of Congress as enemies and that he intended to conduct on attack on the US Capitol," the complaint said. Under surveillanceAccording 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 employees and officials". Cornell had been under surveillance by the FBI since August 2014.The arrest comes in the wake of deadly attacks in and around Paris last week by Islamist gunmen that killed 17 people. The chairperson of the House Committee on Homeland Security applauded the FBI for the arrest and said it was launching investigations the wider scourge of homegrown terrorism."These terrorists are intent on attacking our country and are attempting to convince Americans at home to radicalise, embrace their perverse world view and commit acts of violence," head of the committee Michael McCaul said in a statement. The Republican from Texas said the committee had launched two "full-blown investigations" to look at how the government is fighting domestic threats and how it is protecting itself against "gaps in our defences in order to keep terrorists out of the United States".The Islamic State group, which controls large swathes of territory in Iraq and Syria, has called for Muslims around the world to kill citizens of countries fighting the group, including the United States.