Democratic presidential hopeful Barack Obama addresses a crowd of cheering supporters in Minnesota Tuesday after U.S. media projected he had won enough delegates to secure the party's nomination. (Chris Carlson/Associated Press)Barack Obama won enough delegates on Tuesday to secure the Democratic presidential nomination, according to several U.S. media projections, while his rival Hillary Clinton said she would not make an immediate decision on what course her campaign would take.

"Our primary season has finally come to an end," Obama told a charged crowd of supporters in Minnesota on Tuesday evening. "Because of you, tonight, I can stand before you and say that I will be the Democratic nominee for President of the United States."

The Illinois senator, who was also the projected winner of Tuesday's state primary in Montana, appears set to become the first African-American to be named a major party's presidential nominee when the Democrats formally select their candidate at the national convention in Denver in August.

Obama also offered praise for Clinton, saying she has "an unyielding desire to improve the lives of ordinary Americans, no matter how difficult the fight may be."

"Senator Hillary Clinton has made history in this campaign not just because she's a woman who has done what no woman has done before, but because she's a leader who inspires millions of Americans with her strength, her courage, and her commitment to the causes that brought us here tonight," he said.

Speaking to supporters in New York earlier in the evening, Clinton stopped short of withdrawing from her bid to become the country's first female president. But the New York senator said she's committed to uniting the Democratic Party to retake the White House in November.

Democratic presidential hopeful Hillary Clinton refused to concede the race on Tuesday, saying she would consult with her campaign staff and party officials before making a decision. (Julie Jacobson/Associated Press)"This has been a long campaign and I will be making no decisions tonight," Clinton said, adding she would consult with staff, supporters and party leaders "with the best interests of our party guiding my way."

A lot of people are asking, 'What does Hillary want,' " she said. "I want what I have always fought for: I want the nearly 18 million people who voted for me to be respected and heard."

Clinton 'open' to VP spot: report

Clinton, who was the projected winner in Tuesday's other primary in South Dakota, also praised her rival, saying Obama "has inspired so many Americans to care about politics and empowered so many more to get involved."

"Our party and our democracy is stronger and more vibrant as a result," Clinton said.

Earlier in the day, Clinton reportedly said she is open to being his vice-presidential candidate if it would help the party.

Ahead of polls closing in the last remaining state primary votes, the Associated Press tally had Obama securing enough delegates to seal his nomination.

The news agency tally is based on primary elections, state Democratic caucuses and delegates' public declarations as well as support from 19 delegates and superdelegates who privately confirmed their intentions to the news agency.

Meanwhile, CNN and MSNBC's tallies, based on their own interviews and projections, had the Illinois senator securing enough votes to win the nomination.

Both tallies include reported intentions of a number of as-yet uncommitted superdelegates — party officials and elected representatives who can make up their own minds on who to support in the nomination race.

Typically, superdelegates who haven't announced for one candidate or another say who they'll be supporting once the final primary votes are cast.

McCain welcomes 'formidable opponent'

Obama also sharply criticized the policies of presumptive Republican nominee John McCain, while praising the Vietnam veteran as "a man who has served this country heroically."

"I honour that service, and I respect his many accomplishments, even if he chooses to deny mine," Obama said. "There are many words to describe John McCain's attempt to pass off his embrace of George Bush's policies as bipartisan and new, but change is not one of them."

Speaking earlier Tuesday evening, McCain welcomed Obama as a "formidable opponent" in the fall campaign for the White House, while also attacking his judgment.

"He is an impressive man, who makes a great first impression," McCain said of Obama in a Tuesday evening speech to supporters in New Orleans. "But he hasn't been willing to make the tough calls, to challenge his party, to risk criticism from his supporters to bring real change to Washington. I have."

The veteran Arizona senator objected to Obama's portrayal of him as "running for President Bush's third term," saying he "disagreed strongly" with the Bush administration's "mismanagement" of the war in Iraq.

"I called for the change in strategy that is now, at last, succeeding where the previous strategy had failed miserably," he said. "I was criticized for doing so by Republicans. I was criticized by Democrats. I was criticized by the press. But I don't answer to them. I answer to you."

Clinton campaign effectively over: staff

Clinton made the comments about being the vice-presidential candidate during a conference call with New York lawmakers, the Associated Press said. During the call, she was asked whether Obama could secure the support of key voting blocs if she was his running mate.

"I am open to it," Clinton said, if it would help the party's prospects in November.

Clinton campaign officials who spoke to AP earlier in the day said her campaign was effectively over, but she will pledge to continue to speak out on issues like health care.

Most campaign staff will be let go but paid through June 15, said the officials, who spoke on condition of anonymity because they were not authorized to divulge her plans.

The advisers said Clinton has made a strategic decision not to formally end her campaign, giving her leverage to negotiate with Obama on various matters, including a possible vice-presidential nomination. She also wants to press him on issues he should focus on in the fall, such as health care.

Universal health care, Clinton's signature issue as the president's wife in the 1990s, was a point of dispute between Obama and the New York senator during their epic nomination fight.

With files from the Associated Press