US Senator Barack Obama has won the Democratic party presidential primary in Mississippi, defeating his rival for the nomination, Hillary Clinton.
It is the last contest in the closely fought race until the influential Pennsylvania primary.
Exit polls from Mississippi showed Democratic voters divided sharply along race lines.
More than 90% of the African-American vote went to Mr Obama while 72% of the white vote went to Mrs Clinton.
It was widely predicted that the large African-American vote in the state would deliver it for Mr Obama and last night he won close to 60% of votes cast.
It was also announced last night that Senator Obama had won the caucus portion of last week's election in Texas. Senator Clinton won the primary.
That leaves Senator Obama ahead in terms of delegates.
The next primary is in Pennsylvania in six weeks' time. Both candidates have already been campaigning there.
However, it is thought that neither will have the number of delegates necessary to win the party's nomination when the primaries end in June.
This makes it more likely the race will be decided at the party's convention later in the summer.
Republicans were also voting Tuesday. But as Senator John McCain has already clinched enough delegates to be the party's standard-bearer in the November presidential election, there was little question about the outcome. Mr McCain had 79% of the vote with 99% counted.
Meanwhile, the Clinton campaign has announced that Senator Clinton will address Irish-American voters on issues including Northern Ireland and immigration.
Mrs Clinton said she wanted to discuss such issues at the Irish American Presidential Forum.
She said she encouraged both Mr Obama and the Republican presidential nominee, Mr McCain, to take part.
No date or venue for the forum has yet been set.
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