Democratic Senator Hillary Clinton has taken the first step towards running for the US presidency in 2008.
Sen Clinton, 59, wife of former president Bill, announced her move on her website, saying "I'm in to win".
The former First Lady has set up a presidential exploratory committee, testing the waters for a full bid.
Her announcement comes days after African-American Democratic Senator Barack Obama said he had formed an exploratory committee.
In a videotaped and written message on her website, Sen Clinton said it was time "to overcome six years of Bush administration failures.
"The stakes will be high when America chooses a new president in 2008," she said.
"Only a new president can regain America's position as a respected leader in the world.
"This is a big election with some very big questions. How do we bring the war in Iraq to the right end?" she asked, in addition to mentioning several domestic issues, including health care, the environment and "energy independence".
Sen Clinton said she planned to answer questions in web chats on three consecutive nights, starting on Monday.
Her announcement brings to at least seven the number of declared Democratic presidential hopefuls.
The BBC's Matt Frei in Washington says Sen Clinton's announcement has not surprised many but the specific timing of it this week is significant.
He says the senator was thought to want to declare her intensions later in the year, but her hand was forced by the man who is currently capturing the headlines and many of the hearts of the democratic rank and file - Mr Obama.
Sen Clinton would become the first First Lady to seek presidential office, while Mr Obama's entry into the race would raise the possibility of the US having its first black president.
Mr Obama is one of the Democratic Party's rising stars, having electrified the 2004 Democratic convention with a powerful speech.
Sen Clinton is currently serving as a senator for New York, having won a second term by a landslide last November.
Correspondents say that her unbeatable name recognition and unmatched fundraising ability make her a clear front runner for the Democrats.
Yet she is also seen as a divisive figure. Some estimates say one in three Americans would never vote for her.
Our correspondent says Sen Clinton's biggest policy problem is that she supported the Iraq war and at one stage even called for more troops to be deployed there.
Mr Obama's biggest problem is that as a 45-year-old first-term senator in a time of war, he is relatively inexperienced, our correspondent adds.
He says it is very early days but never before has the Democratic Party faced a choice between a black man and a woman.
Meanwhile, Republican senator Sam Brownback on Saturday declared his intention to seek his party's nomination for a 2008 run.
"My family and I are taking the first steps on the yellow brick road to the White House," Sen Brownback was quoted as saying by the Associated Press.
Cool This election I'll finally be old enough to vote, so I'm very glad to know that for my first vote I'll have the opportunity to vote for either a black man or a woman for Democratic candidate. Exciting changes.
"Man is a marvelous curiosity ... he thinks he is the Creator's pet ... he even believes the Creator loves him; has a passion for him; sits up nights to admire him; yes and watch over him and keep him out of trouble. He prays to him and thinks He listens. Isn't it a quaint idea." Mark Twain
In all honesty I though Jesse 'the Body' Ventura was going to run this year but apparently he hasn't.
The problem for Hillary may be that her husband has a far higher profile than she does and she can be easily embarassed by her husband who makes a perfect target for her political opponants.
"there's only one way to win a war: shout, shout, and shout again!" - The Duke of Wellington ((Blackadder - Stephen Fry))
If only she can be looked at as an individual and not as a person tied to Bill. I know that is impossible but it would be interesting to think that way.
I'm excited to see Obama and Clinton duke it out, especially since Obama seems to be following the Howard Dean formula and is recruiting the younger voters. This will definately be an interesting primary.