Hillary Clinton won an overwhelming victory in Sunday's Democratic primary in Puerto Rico, but is still behind Obama in the race.

Barack Obama needs the support of about 50 more delegates to reach the 2,118 delegates needed to secure the Democratic presidential nomination.

Obama's campaign is confident he will gain the necessary votes by the end of the week, after two western states, South Dakota and Montana, hold the last primaries on Tuesday.

Clinton and Obama are competing to represent their party in the November presidential election.

Their race has gone on far longer than the rival Republican Party's nominating process, raising concerns from some Democrats that their party could appear divided.

Some Democratic Party leaders are urging superdelegates to back a candidate this week to avoid prolonging the campaign further.

Superdelegates are party officials and office holders that can support any candidate they choose. They do not have to back the candidate voters in their state have supported.

Both Obama and Clinton say they will help to end the war in Iraq, revive the lagging economy and improve Americans' access to health care.

Barack Obama is an African American who has attracted supporters with his campaign of hope and change. Clinton is the first woman to seriously compete for the U.S. presidential post. She is the wife of former President Bill Clinton, and has wooed voters by saying she has more experience in the White House than Obama.

The Democratic nominee will face Republican Party Senator John McCain in November. McCain is a Vietnam War veteran and says he has the experience to lead a country at war.

Some information for this report was provided by AP and Reuters. By VOA News