Media playback is unsupported on your device Media caption The video shows Rob Ford swearing and extremely angry

Embattled Toronto Mayor Rob Ford has apologised for a video of him making threats to commit "first-degree murder" against an unknown person.

The leader of Canada's biggest city told reporters he had been "extremely inebriated" in the clip, which shows him apparently blowing off steam.

It is the latest video controversy to engulf the mayor, who admitted this week having smoked crack cocaine.

Councillors are stepping up their calls for Mr Ford, 44, to resign.

'Extremely embarrassing'

At the scene First came the admission he'd been drunk in public. Then the confession he'd smoked crack cocaine. And now, a video which shows the mayor ranting, swearing and using threatening language. The mayor said he's sorry, but didn't address many unanswered questions. When was the video recorded, who was he talking to, who was it about - and will there be any more revelations around the corner? Speak to people here - even those who voted for the mayor - and many will say he should step aside, even temporarily, to take care of his personal issues. But as he walked back inside the glass door of his office, he showed no outward signs that he was ready to relinquish power. People here are wondering how sustainable this situation is, especially now that many of Mayor Ford's colleagues and friends at city hall feel he should step aside.

The new footage looks as though it was secretly filmed on a mobile phone.

Robyn Doolittle, the Toronto Star reporter who has been on the story, told CNN the video appeared to have been shot over the summer, based on the context of some of the dialogue.

In the clip, an agitated Mr Ford paces a room gesticulating during a foul-mouthed rant.

The context of the clip is not clear, nor is the target of Mr Ford's wrath.

He vows to rip out the person's throat, poke out his eyes and ensure his victim is dead.

The mayor appears upset at someone who has called him and his brothers "liars, thieves".

"No hold barred, brother," Mr Ford says in a raised voice. "He dies or I die."

An off-camera voice eggs on Mr Ford, saying: "Mike Tyson!"

After viewing the clip outside his office on Thursday, Mr Ford told reporters: "It's extremely embarrassing and I don't know what to say."

"I hope none of you have ever or will ever be in that state," the mayor told members of the media.

"The whole world is going to see it," he said of the clip.

Drink problem

Allegations of drug use by Mr Ford surfaced in May when journalists reported seeing footage of him smoking crack cocaine.

After months of ducking the question, Mr Ford acknowledged on Tuesday for the first time that he had taken the drug "probably a year ago" while in a "drunken stupor".

He said he was "embarrassed" by his behaviour, but vowed to run for re-election.

Media playback is unsupported on your device Media caption Torontonians on their mayor

The mayor has not been charged, but Toronto police say they are in possession of a video that apparently shows Mr Ford smoking crack.

On Sunday, Mr Ford admitted on his radio show that he had a drinking problem.

He acknowledged having been "hammered" at a street festival in August and "out of control" drunk at city hall during St Patrick's Day celebrations last year.

On Thursday, Mr Ford's mother and sister told a local television station he would not resign.

"It isn't like it has affected his work," said Mr Ford's sister, Kathy.

Asked whether she thought her brother was an alcoholic, she responded: "It depends on what you consider an alcoholic."

Mr Ford's mother, Diane, acknowledged her son's behaviour was "not acceptable" as mayor, but said he had done good work for the city.

'Extraordinary times'

"You have to change, you have to show the public that you've changed," she admonished her son. "There's nothing that he can't recover from, and he will recover."

Media playback is unsupported on your device Media caption Rob Ford's apology on Tuesday for smoking crack cocaine: "I was elected to do a job and that's exactly what I'm going to continue doing"

Mr Ford's allies on the city council say they have lost confidence in him.

But officials in North America's fourth-largest city cannot legally remove the mayor unless he is convicted of a crime.

City Councillor Denzil Minnan-Wong, a member of Mr Ford's executive committee, said he would amend a motion he has filed for the city leader to take leave of absence.

The measure would ask Ontario province to pass an unprecedented law to remove the mayor from office.

"Quite frankly extraordinary measures are needed in extraordinary times," the councillor said on Thursday.

"This situation is deteriorating, it's not going away."