In pictures: Key Democratic polls

Barack Obama has declared himself "within reach" of the Democratic nomination for US president after primary votes in the states of Oregon and Kentucky.

His rival, Hillary Clinton, won the Kentucky vote by a large margin and promised supporters she would fight on to the end of the primary season in early June.

Senator Obama was on course for victory in Oregon, leading Senator Clinton by some 16 percentage points.

Mr Obama now has a majority of pledged delegates but he continues to lack support among low-income whites who tend to favour Hillary Clinton.

He chose to hold his election rally in Iowa, in a symbolic nod to the state where he won the opening contest of the presidential primary season in January.

Though few believe Hillary Clinton can now win the Democratic nomination, she almost seems to be more comfortable battling from the underdog position, correspondents say.