CHICAGO (AP) - A suburban Chicago teenager has pleaded not guilty to charges of seeking to join an Al-Qaeda-linked militant group fighting Syrian President Bashar al-Assad's regime.

Abdella Ahmad Tounisi's attorney entered the plea on Wednesday at a federal court in Chicago. The 18-year-old Tounisi stood by her side in orange jail garb, his legs shackled.

The authorities arrested Tounisi in April at O'Hare International Airport as he allegedly prepared for the first leg of a trip to join Jabhat al-Nusrah.

Tounisi pleaded not guilty to attempting to provide material support to a foreign terrorist organisation and lying to federal authorities.

If convicted, he faces a maximum 23-year prison term.