The incident will revive fears that the US faces a wave of attacks like that carried out by a right-wing extremist which destroyed a federal building in Oklahoma City last April, killing 169 people in the worst act of domestic terrorism in the United States' history.
Ellis Edward Hurst, 52, and Joseph Martin Bailie, 40, were to face initial appearances yesterday before a federal magistrate in Reno, Nevada.
The bomb, a 30-gallon plastic drum, was found on 18 December in a parking lot in Reno by a government employee arriving for work. It was packed with ammonium nitrate and fuel, the same type of ingredients used in the Oklahoma City bombing. The fuse to the bomb had been lit, but it went out and the bomb did not detonate.
If it had gone off, the blast would have caused serious damage to the building and cars in the parking lot and could have killed anyone in the vicinity, Bob Stewart, a federal agent, said. Bomb experts dismantled the device before taking samples of its contents for analysis.
The IRS is a frequent target of rhetorical attacks from America's Christian fundamentalist far-right groups. Timothy McVeigh and Terry Nichols, who were arrested for the Oklahoma attack, had been linked to such groups in the past, but no firm link with any organisation was proved.Reuse content