Romney announces presidential run
Former Massachusetts governor Mitt Romney has become the second major Republican to announce a challenge to President Barack Obama in 2012, declaring he will "put America back on a course of greatness".
Mr Romney joins another former governor, Minnesota's Tim Pawlenty, in having established what is known as an exploratory committee, a move that allows the candidates to begin raising money and hiring staff for a run at the Republican nomination.
Mr Romney issued his announcement in a web video shot at the University of New Hampshire, showing his intention to focus on the tiny US state that holds the first-in-the-nation presidential primary vote.
His declaration focused mainly on the troubled American economy and said he had "become convinced that America has been put on a dangerous course by Washington politicians, and it has become even worse during the last two years".
While Mr Romney had been widely expected to run, the timing of his announcement caught many off guard. Polls show him entering the Republican primary fray as the front-runner in what is expected to be a crowded field of candidates. Other likely Obama challengers range from former House of Representatives Speaker Newt Gingrich to House tea party notable Rep Michelle Bachmann, a Minnesotan like Mr Pawlenty.
Mr Romney sought the Republican nomination in the 2008 race that eventually saw Senator John McCain face Mr Obama. Mr McCain's running mate, former Alaska governor Sarah Palin, is often mentioned as a potential candidate this time, but she has been coy about her intentions.
About 12 Republicans' names regularly rise to the top among potential candidates to challenge Mr Obama, who announced last week that he would seek re-election.
Mr Romney, a businessman who ran Salt Lake City's Winter Olympics in 2002, has lined up donors, staff and advisers for his presidential bid.
He has quietly built a by-the-books campaign organisation that is stacked with experienced presidential operatives.