A Canadian paper says it has seen video footage that appears to show Toronto Mayor Rob Ford smoking crack cocaine, but cannot verify its authenticity.
The Toronto Star said two of its reporters were shown the clip by a tipster who tried to sell the video to the paper.
The story emerged after a US online news site ran the same allegation.
The mayor's lawyer, Dennis Morris, has threatened legal action, calling the claim "false and defamatory".
Mr Morris told the Toronto Star that in any video, it was impossible to tell what a person was doing.
"How can you indicate what the person is actually doing or smoking?" Mr Morris told the paper.