Washington  - Hillary Clinton said she has made "no decisions" about her political future and continued to plug her own White House credentials, as rival Barack Obama clinched the Democratic Party's nomination for president on Tuesday.

The former first lady would not concede the five-month-old campaign, only "congratulating Senator Obama and his supporters on the extraordinary race that they have run."

"This has been a long campaign, and I will be making no decisions tonight," Clinton said, drawing loud cheers from a defiant crowd of supporters in New York.

Clinton said she would be consulting with party leaders in the coming days on the way forward and promised to help unify the Democratic Party ahead of November's general election.

But Clinton also continued to argue she was the "strongest candidate" to take back the White House and pointed to her victories in large swing states that will be crucial to the Democrats' chances in November.

"In all of the states you voted because you wanted a leader who will stand up for the deepest values of our party," she said.

Obama on Tuesday passed the mark of 2,118 delegates needed to clinch the party's nomination, becoming the first African-American ever to lead a major US political party into a general election.

But it was Clinton who claimed a final victory in South Dakota's primary on Tuesday night, a surprise victory on the final day of state-by-state election contests that began with Iowa back on January 3.

"Thanks so much to South Dakota - you had the last word in this primary season and it was worth the wait," she said. (dpa)