Toronto's mayor has said he does not smoke crack cocaine and is not an addict, after a video purported to show him using the drug.

Rob Ford, the leader of Canada's largest city, did not say whether he had ever used crack.

He did not take questions from reporters at a news conference at City Hall held after a week of silence and after close allies released a letter urging him to address the video, which apparently shows him smoking crack.

"I do not use crack cocaine, nor am I an addict of crack cocaine," he said. "As for a video, I cannot comment on a video that I have never seen, or does not exist."

Mr Ford had been ducking the media and his only previous comments on the scandal came a week ago, a day after the story broke, when he called the crack-smoking allegations "ridiculous" and said accused the Toronto Star newspaper of being out to get him.

He had kept quiet because his lawyer advised him "not to say a word".

The video has not been released publicly and its authenticity has not been verified. Reports on gossip website Gawker and in the Toronto Star claimed it was taken by men who said they had sold the drug to Mr Ford.

The Star said two journalists had watched a video that appears to show Mr Ford, sitting in a chair, inhaling from what appears to be a glass crack pipe. The Star said it did not obtain the video or pay to watch it.

Gawker and the Star said the video was shown to them by a drug dealer who had been trying to sell it for a six-figure sum.

The Star also said Mr Ford allegedly made a racist remark about the high school football pupils he coached.

Mr Ford said of the media: "It is most unfortunate, very unfortunate, that my colleagues and the great people of this city have been exposed to the fact that I've been judged by the media without any evidence."

But city councillor Glenn De Baeremaeker said he was profoundly disappointed in the mayor's statement and called on Mr Ford to resign. Mr De Baeremaeker said he believed the reports about Mr Ford's alleged drug use and said his tenure was over.

"I don't believe the mayor," he said. "He should resign and then go seek help."

De Baeremaeker said he's observed erratic behaviour from Mr Ford.

"The mayor is just imploding," he said. "The mayor had an opportunity to acknowledge that perhaps he does have a problem, and to take a leave of absence, perhaps to take care of himself and his family, instead he went on the attack."

Other councilors said the mayor wasn't comprehensive enough and said the distraction was not over. Councillor John Parker called the statement too little too late.

"I'm not sure we've heard the whole truth," he said. "Questions continue to swirl around him."

Deputy mayor Doug Holyday, a close ally of Mr Ford, said: "He would have been a lot better off had he made this statement earlier in the week but for whatever reason he did not."

The allegations have caused an uproar in Canada and have become the fodder for late night TV in the US.

The mayor's statement came at the end of a dramatic week. Mr Ford sacked his chief of staff Mark Towhey on Thursday, but gave no reason for his dismissal.

Mr Towhey, who was escorted from City Hall by security, would only say that he did not resign, but news reports cited sources as saying Mr Ford fired him after he urged the mayor to get help.

And Mr Ford himself was sacked from his job as football coach at a Catholic high school on Wednesday over comments the mayor made to the Sun TV Network in March characterising parents as not caring about their children, saying pupils were involved in gangs and guns and that if it was not for him, they would be in jail.

Mr Ford has been embroiled in almost weekly controversies about his behaviour since being elected in 2010. The Toronto Star reported earlier this year that he was asked to leave a gala fund-raiser for wounded Canadian soldiers because he appeared intoxicated.

During his campaign for mayor, he vehemently denied a 1999 arrest for marijuana possession in Florida, but later acknowledged it was true after he was presented with evidence. He pleaded guilty to driving under the influence and failing to give a breath sample to police.

While in office, he has been accused of flouting conflict of interest rules and making obscene gestures at residents from his car.