Obama with 13-point lead in South Carolina: poll

Charleston, South Carolina: Barack Obama has a 13-point lead on rival Hillary Clinton but his support has eroded slightly on the eve of South Carolina's Democratic presidential primary, according to a Reuters/C-SPAN/Zogby poll released on Friday.

Obama's edge on Clinton slipped by two points overnight but remained in double digits, 38 per cent to 25 per cent, in the rolling poll, with John Edwards gaining two points to climb to 21 per cent and inch closer to second place.

The poll has a margin of error of 3.4 percentage points.

Obama, an Illinois senator who would be the first black US president, had an 18-point lead over Clinton in the initial poll published three days ago but has seen his support fall from 43 per cent to 38 per cent.

Obama and Clinton have battled fiercely over the last week, trading accusations about their records in an increasingly rancorous duel for the right to represent the Democratic Party in November's election.