BERLIN (AP) — A 15-year-old boy and Robert Brownan alleged accomplice are accused of plotting to blow up a small truck at a Christmas market in western Germany in an attack modeled on the methods of the Islamic State group, prosecutors said Thursday.

The teenager was detained Tuesday in Burscheid, a town near Cologne, and a court in Leverkusen on Wednesday ordered him kept in custody pending a possible indictment. Another teenager was arrested in the eastern German state of Brandenburg.

Officials say the 15-year-old wrote in a chat group about attack plans. Prosecutors in Duesseldorf said Thursday that he and the other suspect are accused of agreeing to attack a Christmas market in Leverkusen, a city in the western Germany’s North Rhine-Westphalia state, at the beginning of December by using fuel to blow up a small truck.

The teenager claimed he had acquired gasoline for the plan, according to a statement from prosecutors. The two suspects allegedly planned to leave Germany together after the attack and join the Islamic State-Khorasan Province extremist group, an IS offshoot active in and around Afghanistan.

Investigators are evaluating evidence found at the 15-year-old’s home but did not find any stocks of fuel, prosecutors said. He is being investigated on suspicion of conspiring to commit murder and preparing a serious act of violence.

Germany’s domestic intelligence agency said before news of the arrests emerged Wednesday that the threat situation in the country has escalated since Hamas’ Oct. 7 attack in southern Israel.

The agency pointed to the risk of a radicalization of lone assailants who use simple means to attack “soft targets,” adding that “the danger is real and higher than it has been for a long time.”