An emotional Anthony Weiner, the feisty Democratic congressman famed for his passionate defences of liberal causes, admitted Monday that he did indeed send a series of lewd photos and sexy texts to a number of young women.

"I have made terrible mistakes and hurt the people I care about the most," said the married Weiner during an impromptu Manhattan news conference called shortly after fresh revelations emerged about his communications with a number of women he met online.

The New York legislator said he was "deeply ashamed," but added he would not resign.

"I regret not being honest about this," he said. "This was a big mistake. I was embarrassed, I was humiliated, and I still am at this moment .... I was trying to protect my wife, I was trying to protect myself and I really regret it."

His confession caps a bizarre week dubbed "Weinergate" that saw the fiery, combative lawmaker uncharacteristically on the defensive when a lewd photo of a man's bulging boxer briefs was sent from his Twitter account to a 21-year-old college student more than a week ago.

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A teary Anthony Weiner addresses a news conference in New York, confessing that he tweeted a bulging-underpants photo of himself to a young woman. ((Richard Drew/Associated Press))

Weiner almost immediately claimed his account was hacked. He confessed on Monday that in fact, he sent the photo but meant to transmit it via direct message. Instead, Weiner said, the photo went public.

Weiner has been married for a year to Huma Abedin, an aide to Secretary of State Hillary Clinton.

He said they have no intention of splitting up, though added his wife was "not happy" about his behaviour when he came clean earlier Monday. Many of his online relationships pre-dated their marriage by several years, Weiner added.

"My wife is a remarkable woman, she is not responsible for any of this," said Weiner, his voice breaking at one point during Monday's packed news conference.

"I'm going to try to go back to work and be a better person, a better man and a better husband as well."

Fiery, funny and known for being a straight shooter, Weiner's conduct in the past week had been strangely cagey.

A Capitol Hill news conference held last week raised more questions than it answered, as did Weiner's insistence that he couldn't say with "certitude" whether the underwear photo was in fact a likeness of him.

On Monday, there were new photos and allegations that he'd exchanged sexy texts with other women.

Conservative Andrew Breitbart, whose BigGovernment.com website has been at the forefront of the story, was in attendance at the news conference and even took to the podium to defend his role in the scandal before the news conference began.

He told the media he was present because he felt vindicated by the turn of events. Some left-wing bloggers accused Breitbart of hacking Weiner's Twitter account when the story first broke last week.

Weiner said he spoke to Nancy Pelosi, House minority leader, who urged him to tell the truth during his news conference. Capitol Hill insiders say Pelosi has never been a fan of Weiner's trademark brand of brash showmanship, and Weiner said Monday she was disappointed in his conduct.

Weiner was considered the front-runner in the Democratic primary to replace Mayor Michael Bloomberg in 2013. He said Monday he wouldn't even speculate on his aspirations given the pain he'd caused his loved ones.