New York State Governor Eliot Spitzer has apologised amid allegations of involvement in a prostitution ring.
The married father-of-three said he had acted in a way that violated his obligations to his family.
Mr Spitzer, a prominent Democrat who campaigned for ethical leadership, said sorry to his family and the public.
He made no reference to allegations published by The New York Times, which said he had been involved with a high-priced prostitution service.
"I have disappointed and failed to live up to the standard I expected of myself," the first-term governor told a packed press conference at his Manhattan office.
"I must now dedicate some time to regain the trust of my family," he added, as his wife of two decades, Silda, stood by his side.
He declined to answer questions as to whether he would resign but said he would report back "in short order".
Last week, four people were arrested in connection with the alleged prostitution ring, the New York Times reported.
As part of the investigation, a federal wire-tap on a Washington hotel last month had recorded Mr Spitzer allegedly arranging to meet a prostitute, the newspaper added.
Mr Spitzer, 48, had abruptly cancelled Monday afternoon appointments to meet senior advisors about the allegations, the Times reported.
According to court papers, the investigation involves an exclusive prostitution ring called the Emperor's Club VIP, which operated in cities across the US, as well as in London and Paris.
More than 50 prostitutes were employed by the ring, charging fees ranging from $1,000 to more than $5,500 an hour, prosecutors said last week.
The BBC's Matthew Price in New York says things do not look good for Mr Spitzer at the moment.
Although he has not confirmed that the allegations are true, Mr Spitzer looked deeply uncomfortable as he spoke to the media, our correspondent says.
He will need the help of his many influential connections within the Democratic Party if he is to hope to survive the scandal and make a comeback, our correspondent adds.
The Republican minority leader of the New York state assembly, James Tedisco, called for Mr Spitzer to resign "immediately".
"Today's news that Eliot Spitzer was likely involved with a prostitution ring and his refusal to deny it leads to an inescapable conclusion: he has disgraced his office and the entire state of New York," Mr Tedisco said.
The Republican Governors' Association also reacted quickly to the allegations, calling for Mr Spitzer to step down.
"Eliot Spitzer campaigned on ethics reform; unfortunately the governor of New York has egregiously failed his constituents," said the group's executive director Nick Ayers.
"The governor of New York should immediately resign from office and allow the people of New York to pursue honest leadership."
The scandal could prove embarrassing for New York Senator Hillary Clinton, who is competing with rival Barack Obama to be the Democratic Party's choice to run for president.
Mr Spitzer has promised to support Mrs Clinton's presidential bid
A close ally of Mrs Clinton, Mr Spitzer has pledged to support her campaign.
He is one of the 796 super-delegates - party leaders and elected officials - who will vote on which candidate to back at the Democrats' national convention in August.
Mr Spitzer was elected governor in November 2006, promising ethical reform in New York.
As New York's attorney general, he had become known as the Sheriff of Wall Street for his relentless pursuit of financial wrong-doing.
His successes in that battle led Time Magazine to name him "Crusader of the Year" in 2002.
Mr Spitzer had also taken a firm line against prostitution in New York.