US Democratic presidential candidate Senator Barack Obama (D-IL) smiles during a town hall-style meeting at Troy High School in suburban Detroit, June 2, 2008. (Xinhua/Reuters Photo) 

US senator Barack Obama clinched the Democratic presidential nomination Tuesday night, but his rival senator Hillary Clinton said she hasn't made decision about the future of her campaign.

Based on the latest tally of all US media organizations, Obama now has passed the threshold of 2,118 national convention delegates needed to clinch this year's Democratic nomination, becoming the first African-American presidential nominee of a major US party.

"Tonight, I can stand before you and say that I will be the Democratic nominee for president of the United States," Barack Obama said in a prepared speech to be delivered at a rally in St. Paul, Minnesota.

"Tonight we mark the end of one historic journey with the beginning of another – a journey that will bring a new and better day to America," he said.

Trying to unite the party as quick as possible, he praised his rival senator Hillary Clinton.

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

"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.