The Swedish panel that awards the Nobel medicine prize says its secretary-general, Urban Lendahl, has resigned because of an investigation into disputed stem-cell scientist Paolo Macchiarini.

Ann-Mari Dumanski, a spokeswoman of the Nobel Assembly at Karolinska University, confirmed Monday that Saturday's resignation took effect immediately, but gave no details. The Nobel panel said on its website that the professor resigned "out of respect for the integrity of the Nobel Prize work," and because he might become involved in the investigation.

Lendahl was one of several professors at Karolinska who in 2010 recommended hiring Macchiarini. Last week the university decided to investigate Macchiarini after a Swedish documentary raised ethical concerns about operations performed by him.