A Massachusetts man accused of plotting to kill Americans was portrayed by federal prosecutors Thursday as a jihadist who is too dangerous to be released on bail, but the man's lawyer said he was charged only after he refused to become an FBI informant against Muslims.

Tarek Mehanna, 27, of Sudbury, was arrested a year ago and charged with lying to the FBI. New, more serious charges were added last month, when Mehanna was accused of conspiring with two other men to shoot shoppers at U.S. malls, to kill two unnamed prominent U.S. politicians and to kill American soldiers in Iraq.

Authorities said he and the other men never came close to pulling off an attack, but did seek training at terrorist camps in the Middle East. The men allegedly told friends they were turned down for terrorist training because of their nationality, ethnicity or inexperience, or that they were unable to make contact with people they hoped would get them into such camps.

The men abandoned plans to attack malls because their weapons contact said he could find only handguns, not automatic weapons, prosecutors allege.

During a detention hearing in federal court on Thursday, Magistrate Judge Leo Sorokin heard arguments from prosecutors and Mehanna's defense on whether he should be kept behind bars until his trial. Sorokin did not immediately rule.

Assistant U.S. Attorney Aloke Chakravarty urged the judge to hold Mehanna without bail, saying he poses a danger to the community and is likely to flee before his trial because he faces a possible sentence of life in prison.