Greenpeace environmental activists have dumped a truckload of coal at the doorstep of France's presidential palace just hours before a visit by German Chancellor Angela Merkel.

The activist group's French wing said on its website that the pre-dawn action Wednesday also involved containers of nuclear waste inside the truck. Images on the site showed police alongside at least four women activists wearing T-shirts written in German and French.

A Paris police spokeswoman declined immediate comment. A presidential palace official wasn't immediately available for comment.

The stunt raises new questions about security in front of France's presidential Elysee palace — normally guarded visibly by at least several police. Greenpeace France has recently carried out acts including peaceful invasions of French nuclear sites in a bid to expose security dangers.