AFP - German prosecutors raided the headquarters of sportscar maker Porsche on Thursday and seized documents in an insider trading investigation, the company said.

Porsche gave few further details but the Die Welt daily reported that the probe centred on former executives including Wendelin Wiedeking, who resigned as CEO last month after failing in his bid to acquire Volkswagen.

"On Thursday morning, officers from Stuttgart prosecutors entered the company's offices with search warrants ... the prosecutors suspect a breach of public disclosure requirements and market manipulation," the firm said in a statement.

"Porsche denies the accusations. The company will cooperate with the prosecutors and is fully supporting the investigating officers in order to contribute to a swift clearing-up of the matter."

Under Wiedeking, Porsche built up a 51-percent stake in the much larger VW and wanted to take full control but the attempt failed and left Porsche squeezed under a huge debt pile. The two firms now plan to merge.

In the course of the takeover battle, VW shares soared but in recent days they have fallen back sharply as the takeover premium has unwound.