Washington  - Barack Obama declared himself the Democratic Party's candidate for president after clinching the nomination Tuesday night, showering praise on his rival Hillary Clinton and setting his sights on a general election fight against Republican John McCain.

"Tonight, I can stand here and say that I will be the Democratic nominee for president of the United States," Obama told a rally in St Paul, Minnesota.

"Tonight we mark the end of one historic journey with the beginning of another," he said, exactly five months after the party's nomination process began in Iowa and more than a year since announcing his bid to become the first African-American president.

Obama said he was convinced the Democratic Party would unite ahead of November and praised Clinton - who had hoped to become the first woman president - for a "barrier-breaking campaign."

"Our party and our country are better off because of her and I am a better candidate for having had the honour to compete with Hillary Rodham Clinton," he said.

The 46-year-old Illinois senator also laid out his general election strategy, sharply criticizing McCain for towing the line of the unpopular President George W Bush and suggesting his opponent had not run a respectful campaign to date.

"I respect his many accomplishments, even if he chooses to deny mine," Obama said of McCain.

Obama earlier Tuesday passed the mark of 2,118 delegates needed to clinch the Democratic Party's nomination.

Obama sounded many of the notes that have carried his presidential campaign over the last year, promising unity, calling for change in Washington and offering to bring "new energy and new ideas to the challenges we face."

"This was the moment, this was the time when we came together to remake this great nation so that it may always reflect our very best selves," he said. (dpa)