The boy had started to become "radicalised" in autumn 2023, the court said.
A German court on Friday sentenced a 15-year-old boy to four years in jail for planning an Islamist attack on a Christmas market in the western city of Leverkusen.
The teenager wanted to rent a truck and "kill as many people as possible" by ramming it into the traditional market, the court in Cologne said in a statement.
The boy had started to become "radicalised" in autumn 2023, the court said.
The evidence against him included a video in a chat group announcing his plans for an attack on "infidels" with a recognisable Islamist symbol in the background.
The boy had planned the attack along with another teenager who was supposed to film it and share the video, the court said.
The 16-year-old from Brandenburg, the state that surrounds Berlin, will stand trial in a different court from July.
The 15-year-old made a "comprehensive confession" during his trial, a court spokesman told AFP.
Islamist extremists have carried out several attacks in Germany in recent years, the deadliest being a truck rampage at a Berlin Christmas market in December 2016 that killed 12 people.
More recently, an Islamist motive is suspected in the killing of a police officer in a knife attack on the market square in the city of Mannheim in late May.
The number of people considered Islamist extremists in Germany fell slightly from 27,480 in 2022 to 27,200 last year, according to a report from the federal domestic intelligence agency.
However, in presenting the report, Interior Minister Nancy Faeser said Germany would be "continuing to step up the fight against Islamist terrorism".
In another case involving teenagers, two boys and two girls aged 15 to 16 were arrested at Easter this year on suspicion of planning an Islamist attack in the same region of western Germany.
Herbert Reul, interior minister of North Rhine-Westphalia state, said the young age of the suspects left him "speechless", adding that it posed a "huge challenge for society as a whole".
Germany's biggest-selling daily Bild reported that the four youths were allegedly planning to carry out Molotov cocktail and knife attacks in the name of the Islamic State group.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)