The FBI has arrested two women on suspicion of planning a terrorist attack, similar to the Boston bombing.
A Brooklyn court charged Asia Siddiqui and Noelle Velentzas with conspiracy to use weapons of mass destruction.
The two women, US citizens, spoke only to say they understood the charges.
They had referred to themselves as "citizens of the Islamic State", prosecutors allege, and Ms Siddiqui had several gas tanks and instructions on turning them into bombs.
"My client will enter a plea of not guilty, if and when there is an indictment. I know it's a serious case, but we're going to fight it out in court," said Ms Siddiqui's lawyer, Thomas Dunn.
Ms Siddiqui "had repeated contact with members of the foreign terrorist organisation al-Qaeda in the Arabian Peninsula" the court documents said.
Her accomplice, Ms Velentzas, referred to Osama Bin Laden as a hero, according to the US Department of Justice.
"The defendants allegedly plotted to wreak terror by creating explosive devices and even researching the pressure cooker bombs used during the Boston Marathon bombing," said Assistant Director in Charge Diego Rodriguez, of the FBI's New York Field Office.
The justice department said the two women have plotted to build an explosive device since at least August of last year and studied chemistry and electricity.
They did not have a specific target but at one point considered Herald Square in Manhattan, according to the court documents.
Ms Velentzas apparently criticised a US Air Force veteran who was recently arrested for attempting to travel to Syria engage in violent jihad.
She questioned why people would try to travel overseas when there were targets in the US that provided opportunities for "pleasing Allah", the justice department said.
The documents say the women have been meeting with an undercover agent for several years.
Last month, officials announced that they had charged 47-year-old Tairod Nathan Webster Pugh, a US citizen and a veteran of the US Air Force, for allegedly trying to provide material support to the Islamic State.
Mr Pugh has denied all of the charges.