Congratulating Barack Obama on becoming the first African-American to lock up the Democratic presidential nomination, Secretary of State Condoleezza Rice [Images] described his candidature as an "extraordinary expression of inclusiveness".

Rice, who is the highest ranking black official in President Bush's cabinet, also called the development as a landmark for equal rights for the African-American community in the country, after more than two centuries of struggle.

"The United States is a country that has overcome many, many, now years, decades, actually a couple of centuries, of trying to make good its principles," Rice, who has been mentioned as a possible running mate for Republican Presidential candidate John McCain, said.

"And I think that what we're seeing is, an extraordinary expression of the fact that 'we the people' is beginning to mean all of us," she said, referring to the opening line of the US constitution.

Obama secured support of the required number of delegates to clinch the Democratic nomination, after a long-drawn often bitter contest with senator Hillary Clinton.

The 46-year-old Harvard-educated first-time Senator from Illinois will contest Republican McCain in the Presidential election in November, becoming the first black candidate to lead a major party into a campaign for the White House.