A Massachusetts man sentenced to more than 17 years in federal prison on terrorism-related charges is appealing his conviction.

A lawyer for 32-year-old Tarek Mehanna, of Sudbury, said in a filing Tuesday in U.S. District Court in Boston that Mehanna's sentence should be vacated because prosecutors withheld information about a key government witness during his 2011 trial.

An appeals court upheld Mehanna's conviction on providing material support to al-Qaida. The U.S. Supreme Court last year decided not to review the case.

Prosecutors said he traveled to Yemen seeking terrorist training and intended to fight U.S. soldiers in Iraq. When that failed, they said, he returned home and promoted violent jihad online.

Mehanna's lawyers said he didn't give any tangible support to al-Qaida, and his online activities were protected free speech.