Voters are casting ballots Tuesday in the U.S. states of Kentucky and Oregon, where Democrats Barack Obama and Hillary Clinton continue the race for their party's presidential nomination.

Opinion polls show Clinton with a wide lead in the East Central state of Kentucky, while Obama is favored in the northwestern state of Oregon.

After the results are counted, Obama is expected to have a majority of the pledged delegates needed to win the nomination.

Clinton also trails Obama in the race for so-called superdelegates, party officials and elected office-holders who are free to vote for any candidate at the party's nominating convention.

But, Clinton insists the contest is not over. In a note to reporters, her campaign said any effort by Obama to declare victory after today's contests will be a "slap in the face" to Clinton supporters.

Obama has recently turned his focus to the upcoming general election against presumptive Republican nominee John McCain.

McCain and Obama have been sparring over foreign policy regarding Iran.

On Monday, McCain, criticized the Democrat for wanting talks with Iran without precondition.

He also took issue with Obama's statement that the threat posed by Iran is tiny compared to the threat once posed by the Soviet Union.

Obama, the frontrunner for the Democratic Party presidential nomination, responded by saying he has made it clear that Iran poses a grave threat, but insisted that diplomacy is appropriate. He accused McCain of seeking to continue the failed policies of President George Bush.

Some information for this report was provided by AFP, AP and Reuters.