A man has been charged with terrorism-related offences that include plotting to kill people in a US shopping centre, the US Justice Department says, BBC reported.
Tarek Mehanna, 27, was held in Sudbury, a suburb of Boston, Massachusetts, and charged with conspiracy to provide material support to terrorists.
He is also accused of plotting to kill two US politicians and people overseas, and of seeking terrorist training.
At least two other co-conspirators were involved, officials said.
One was named as Ahmad Abousamra, who the authorities say is now in Syria.
Mr Mehanna, who is reported to be a US citizen, was arrested at his home on Wednesday morning.
'Violent jihad'
Detailing the charge against Mr Mehanna, US prosecutors accused him and his alleged co-conspirators of discussing how to obtain automatic weapons before "randomly shooting people in a shopping mall".
They allegedly discussed "the logistics of a mall attack, including co-ordination, weapons needed and the possibility of attacking emergency responders", acting US Attorney Michael Loucks said.
However, the plan was eventually abandoned, prosecutors said, because the conspirators could not get hold of the necessary weapons.
The charge alleges that from about 2001 to May 2008, Mr Mehanna conspired with others, plotting to provide material support and resources for use in carrying out a conspiracy to kill, kidnap, maim or injure persons or damage property in a foreign country and the killing of US nationals outside the US.
"They discussed their desire to participate in violent jihad against American interests and that they would talk about fighting jihad and their desire to die on the battlefield," he said.
They allegedly attempted to inspire each other and radicalise others by watching and distributing jihadi videos.
Mr Mehanna and two of his associates also allegedly travelled to the Middle East in February 2004 hoping to attend a terrorist training camp, with the aim of fighting US and allied forces in Iraq, but did not succeed in finding one to join.
A justice department document said that while "some of these plans involved no more than one or two conversations, at least one involved multiple conversations, discussions and preparations".
Mr Mehanna was previously arrested in 2006, when he was charged with lying to the FBI about the whereabouts of Daniel Maldonado, a man convicted of training alongside al-Qaeda members, Associated Press reported.