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LONDON, England (CNN) -- Gordon Brown has launched his campaign to be Britain's next prime minister, a day after Tony Blair announced he would stand down in June. Earlier, Blair delivered a ringing endorsement of Brown, who has served as his finance minister since 1997.
Brown unveiled his manifesto on Friday in a speech to activists of the ruling Labour Party, promising Britain would maintain its obligations to the Iraqi people and that government must be more accountable to parliament in all matters, including war.
The 56-year-old Scot, who faces no serious opposition to succeeding Blair as Labour leader and therefore prime minister, used the speech to challenge political rivals and highlight his vision for the future of Britain.
The chancellor of the exchequer discussed the moral principles at the basis of his political beliefs and focused on "new insecurities" of climate change and terrorism, issues worrying voters today.
Standing at a podium in front of a banner that read, "Gordon Brown for Britain," Brown said: "Today I announce that I am a candidate to be the leader of the Labour Party and to lead a new government."
His announcement came the day after Blair ended months of speculation by saying he will leave 10 Downing Street on June 27. (Full story)
Brown said Blair had served Britain with distinction, adding "in the weeks and months ahead, my task is to show that I have the new ideas, the vision and the experience to earn the trust of the British people. Today there are new priorities and I offer new leadership for a new time."
The outgoing PM in turn put his weight behind Brown earlier Friday, backing his long-time friend and rival with a strong endorsement.
"I'm absolutely delighted to give my full support to Gordon as the next leader of the Labour Party and prime minister," Blair said. "I will endorse him fully.
Brown is "an extraordinary and rare talent," Blair said, adding that he was perhaps the most successful chancellor in British history. (Watch profile of Gordon Brown .)
But with the Iraq war severely denting Labour's popularity, Brown on Friday appeared to distance himself from Blair's foreign policy.
The chancellor accepted "that mistakes have been made" in Iraq, and said he would visit the region to hear from the government and people on the ground. Brown said this would be one of his first acts as prime minister.
He also said more must be done on the cultural, political and ideological fronts to counter al Qaeda influence and prevail in the "battle of hearts and minds."
He indicated that such an effort would help Iraq's moderate Muslim community. "We will keep our obligations to the Iraqi people. We will listen and we will learn from what mistakes have been made," he said.
Brown has always been considered the favorite to succeed Blair and on Thursday won White House support. (Your views)
U.S. President George Bush said he looked forward to meeting Brown, who he called "an open and engaging person" who "understands the consequences of failure" in Iraq.
There has been much speculation that as prime minister, Brown would form a more distant relationship than Blair with Bush, particularly over Iraq.
And some Westminster observers believe he will move quickly to withdraw the remaining UK troops from the country.
But Jack Straw, Brown's campaign manager, said he did not expect any great foreign policy change.
"You are not going to get a dramatic shift here, but of course you will get a different style of leadership," he told the BBC.
But CNN's European Political Editor Robin Oakley said Brown was unlike his predecessor Blair, the "ultimate showbiz politician."
Oakley said Brown was much more serious, took his time to make decisions and was a very controlling leader.
While Brown had a good grounding in running a key ministry, Oakley said he might not have the patience to handle the diplomatic juggling needed to be PM.
Three candidates have put their names forward to lead the Labour Party: Brown, and two left-wing candidates, John McDonnell and former environment minister Michael Meacher.
Candidates must win the support of 44 Labour MPs by May 16: if they fail to reach this threshold, they must drop out. Brown is expected to easily secure this number of backers but it is doubtful whether McDonnell or Meacher will do do.
The selection process -- which includes a vote of Labour lawmakers, party members and members of affiliated trade unions -- will then take six to seven weeks, with confirmation by a party conference at the end of June.
Blair will then formally submit his resignation to Queen Elizabeth II, clearing the way for Brown, if the winner, to take over as Britain's leader. Given Labour's majority in the House of Commons, the change does not require an election.
Gordon Brown poses with his wife Sarah at his campaign launch in London on Friday.