US Democratic presidential candidate Barack Obama (D-IL) and his wife Michelle prepare to board their plane at Chicago Midway Airport June 3, 2008, en route to his final primary night rally in St Paul. (Xinhua/Reuters Photo)

The event, held in the same site where Republicans will gather for their national convention this summer, also marked the beginning of Obama's general election campaign to take on his Republican opponent John McCain.

Speaking in New York, Clinton congratulated Obama for his campaign, but she did not concede the race nor discuss the possibility of running as vice president.

There were reports earlier in the day that she would concede, but her campaign said she was "absolutely not" prepared to do so.

"This has been a long campaign and I will be making no decisions tonight," she said.

Clinton said she would meet with supporters and party leaders in the coming days to determine her next steps.

She also asked people to go to her website to "share your thoughts with me and help in any way that you can."

Tuesday is the last day of this year's Democratic presidential primary season with contests being held in Montana and South Dakota.

There are 16 pledged delegates at stake in Montana and 15 in South Dakota.

Preliminary results show Obama won Montana and Clinton carried South Dakota, a result that has no impact on the outcome of the nomination race.

(Xinhua News Agency June 4, 2008)