FRANKFURT, Germany (AP) — Prosecutors say law enforcement officials have conducted searches at German automaker Opel as part of an investigation into suspected manipulation of diesel emissions.

The dpa news agency reported that investors went to company facilities Monday in Russelsheim and Kaiserslautern. Nadja Niesen, a spokeswoman for prosecutors in Frankfurt, was cited by dpa as saying investigators suspect Opel may have used software to turn off emissions controls at certain engine speeds and temperatures.

Opel, which is part of France's PSA Group, confirmed the searches but declined to offer details.

Diesel came under scrutiny in Europe after Volkswagen admitted illegally manipulating software to cheat on emissions test. Cars from other automakers were subsequently found to turn off controls at certain temperatures, ostensibly to protect the engine but also increasing emissions.