New York mayoral candidate Anthony Weiner has admitted sending explicit messages to a woman, two years after he left Congress over a similar affair.
An unnamed woman told website The Dirty she had an online relationship with the 48-year-old last year.
Mr Weiner, who has been leading polls of Democratic mayoral candidates, said he was "very sorry".
In 2011, he said his Twitter account was hacked, but then admitted sending lewd photos to young women.
Flanked by his wife, Huma Abedin, at a press conference on Tuesday in New York, he apologised while reading from a prepared statement.
He also said he would not drop out of the city's mayoral race, which will be decided by voters in November. Three of his rivals immediately called on him to stand aside.
'Horrible mistakes'
Mr Weiner told reporters: "This behaviour is behind me. I've apologised to my wife, Huma, and I'm grateful that she has worked through these issues with me and that I've had her forgiveness.
"I want to again say how very sorry I am to anyone who was on the receiving end of these messages and the disruption that this has caused."
He said some of the latest reports were inaccurate, but refused to go into detail.
Ms Abedin then took to the podium and said: "Our marriage, like many others, has had its ups and its downs. It took a lot of work and a whole lot of therapy to get to a place where I could forgive Anthony."
She continued: "Anthony's made some horrible mistakes, both before he resigned from Congress and after. But I do very strongly believe that it's between us and our marriage."
"I love him, I have forgiven him, I believe in him," she added.
'Carlos Danger'
Briefly taking questions after the statements, Mr Weiner admitted that some of the online activity in question had taken place as late as summer last year.
The woman at the centre of the latest allegations has said they began exchanging messages in July 2012 and continued for six months.
She said she was 22 years old when they made contact on the social networking website Formspring.
The woman claimed Mr Weiner had used the alias "Carlos Danger" for their racy exchanges.
"I was young and dumb," The Dirty quoted her as saying.
"I just want people to really know he's lying when he acts like he has changed."
Mr Weiner has previously said he should not have denied posting lewd photos on Twitter in 2011.
He said he only did so because he wanted to keep the truth from his then-pregnant wife, who is a former adviser to Hillary Clinton.
She gave birth to the couple's son, Jordan, later that year.
Mr Weiner will find out how damaging his latest conduct has been in September's primary elections, when Democratic voters decide if he or one of his rivals should represent their party in the mayoral race.
He is not the only disgraced politician aiming for a comeback.
Two weeks ago, former New York Governor Eliot Spitzer - who resigned in 2008 after admitting to paying for sex with prostitutes - announced his candidacy for city comptroller.
据BBC今天凌晨的消息，两年前由于“猥亵照”事件离开美国国会的前议员安东尼·韦纳，作为下届纽约市长的热门人选，近日又爆出了“艳照门”，他承认曾在社交网站上发送露骨信息给一名年轻女子。
在妻子胡玛·阿贝丁的陪伴下，安东尼·韦纳于本周二在纽约举行了新闻发布会，宣读了事先准备好的讲稿，并就自己的所作所为致歉。
“我现在早已痛改前非。我已经向我的妻子胡玛道过歉了，非常感激她始终不离不弃地陪伴着我经历这一切，并且原谅了我。对于那些看到我照片的人，很抱歉打扰了你们的生活，我再次向你们道歉。”安东尼在发布会上说。
据指控安东尼的女子称，她和安东尼于2012年7月起开始在社交网站Formspring上互发信息，当时她22岁。安东尼将他们间的猥亵对话称作“卡洛斯危险”，这种关系一直持续了半年。
“我只是想告诉大家，他虽然表现得好像已经洗心革面了，但其实只是在欺骗大众。”这名女性告诉The Dirty网站的记者。
2011年，安东尼曾爆出在推特上发布猥亵照片的丑闻，但当时他称自己账号被盗，后来又承认确有此事，并声明此前之所以否认是因为不希望刺激当时有孕在身的妻子。
在今年九月即将进行的纽约市长初选中，安东尼将深刻意识到这次“艳照门”所带来的恶劣影响。届时，民主党选民将决定他或者其竞争对手是否能够代表他们的政党参与市长竞选。