A US man allegedly planning to engage in terrorism in Syria was arrested at a Chicago airport after months of surveillance, the FBI said.
There is "no connection between this case and the events that occurred over the last several days in Boston," the Federal Bureau of Investigation said in a statement.
Agents had been monitoring Abdella Ahmad Tounisi, 18, for some time due to his friendship with a man who was arrested in September after a botched attempt to detonate a bomb outside a Chicago bar.
While Tounisi discussed that plot with his friend, Adel Daoud, a criminal complaint stated that he did not participate, in part because he correctly guessed that Daoud was working with an undercover agent.
Even after he was questioned following the arrest of his friend, Tounisi continued to search online about martyrdom operations and violent jihad, the charging papers said.
He eventually happened upon a website set up by the FBI to look like a recruiting page for the al Qaeda-affiliated Jabhat al-Nusrah and spent about three weeks making plans with an undercover agent.
Tounisi was arrested at 8:29 pm Friday while waiting at the gate to board a flight to Istanbul.