Officials said the man did not appear to be targeting Trump or others involved in the trial
The video was posted by Amaq news agency a day after two men burst into the Catholic church in Normandy during a service, forced the priest to his knees and slit his throat.
The two men who identified themselves as Abu Omar and Abu Jalil el-Hanafy appeared in the one-minute video sitting on a staircase pledging loyalty to Abu Bakr al-Baghdadi, Islamic State's leader.
One of the two attackers has been named as 19-year-old Adel Kermiche, who was under close surveillance after two failed attempts to reach Syria last year, France's anti-terrorism prosecutor said on Wednesday
The second attacker remains unidentified. Police shot and killed both assailants as they emerged from the church.