A German opposition party says one of its leaders' immunity from prosecution has been lifted amid an investigation by prosecutors after he was filmed with a cannabis plant on his balcony.

The Greens said Sunday that co-chairman Cem Ozdemir's parliamentary immunity from prosecution was lifted last month. The Bild am Sonntag newspaper reported that Berlin prosecutors opened an investigation into suspected growing of drugs after an Ice Bucket Challenge video last summer showed Ozdemir dousing himself in cold water with a cannabis plant in the background.

Prosecutors couldn't immediately be reached for comment Sunday.

Ozdemir said prosecutors had been in touch with him. He advocates legalizing cannabis and said it's "high time" to follow the example of some U.S. states and put the issue on the German Parliament's agenda.