WASHINGTON (Reuters) - President Barack Obama has extended his narrow lead over Republican challenger Mitt Romney among likely voters in a race that remains statistically tied nine days before the election, according to a Reuters/Ipsos tracking poll released on Sunday.

WASHINGTON (Reuters) - President Barack Obama has extended his narrow lead over Republican challenger Mitt Romney among likely voters in a race that remains statistically tied nine days before the election, according to a Reuters/Ipsos tracking poll released on Sunday.

Obama has a 49 percent to 46 percent edge over Romney, marking a 1 point increase from Saturday but still within the daily online survey's 4 percentage-point credibility interval for likely voters.

Swings could be possible in the remaining days of the campaign, however. Fifteen percent of registered voters say they could still change their minds and vote for a different candidate.

The precision of Reuters/Ipsos online polls is measured using a credibility interval. In this case, the poll has a credibility interval of plus or minus 4.0 percentage points for likely voters.

(Editing by Alistair Bell and Eric Beech)