FRANKFURT — German prosecutors said on Tuesday that they had expanded their investigation into the illegal manipulation of tailpipe emissions by Volkswagen, raising the number of suspects to 17, from six.

In line with German privacy rules, none of the suspects’ names were disclosed.

So far, no suspects are current or former members of the company’s management board, said Klaus Ziehe, a spokesman for the state’s attorney’s office in Braunschweig, a city near Volkswagen headquarters in Wolfsburg.

But Mr. Ziehe said that the investigation was continuing, and that prosecutors had not ruled out involvement by top management. “We are looking at all levels, including the management board level,” he said.

Mr. Ziehe declined to say what kinds of jobs the suspects held or where in the company they worked.

Volkswagen did not immediately respond to a request for comment.