Berlin (AFP) - Germany's domestic security service is investigating an acid attack on a manager of an energy company that has been in conflict with environmental protesters, police said Monday.

Two unidentified males on Sunday hurled acid at the face of Bernhard Guenther, 51, chief financial officer with Essen-based company Innogy, the renewables subsidiary of energy giant RWE, said police.

Bild daily reported that the attackers used sulphuric acid, badly injuring the victim's face and eyes, as he was walking back from a bakery though a park close to his home in Haan near Duesseldorf.

While the suspects, believed to be aged in their 20s, ran off, Guenther managed to walk the remaining 200 metres (600 feet) to his luxury home, where he called emergency services.

He was taken by ambulance helicopter, with the paramedics wearing protective suits and gas masks, to a specialist clinic where he was reportedly in a stable condition Monday.

"We are deeply shocked," said Uwe Tigg, chief of Innogy, which also declared that so far there was "no information on the motivation for the attack".

"The incomprehensible attack on Bernhard Guenther has hit us deeply," said the CEO of RWE, Rolf Martin Schmitz, adding that management and employees were "dismayed and appalled".

Police launched an attempted murder probe and were investigating whether the attack may have been related to Guenther's personal or professional life.

Bild daily reported that the domestic security service, which is in charge of politically motivated crime, was investigating.

RWE has long been engaged in a battle with environmentalists over its open-pit coal mining operations, including at the flashpoint forest site Hambacher Forst where activists have lived in a protest camp for years.