Barack Obama and Mitt Romney are now tied in the US presidential race, according to a Reuters/Ipsos daily tracking poll released today.

The online survey of likely voters found Mr Obama and Mr Romney were each supported by 46% of the electorate ahead of their final televised debate, which takes place tonight (2am Irish time).

Mr Romney trailed by 1 percentage point when the poll was last published, on Saturday.

The two candidates have remained within three percentage points of each other since shortly after their first debate on 3 October.

"Today's number emphasises the fact that the race is very close. We enter the final debate with the candidates literally neck and neck," Ipsos pollster Julia Clark said.

However, Mr Obama still holds a substantial advantage in the battleground states that will determine the outcome of the 6 November election.

Ipsos projects that Mr Obama will carry hotly-contested states such as Florida, Ohio and Virginia, for a total of 325 electoral votes to Mr Romney's 213 electoral votes.

Reuters/Ipsos online polls are measured using a credibility interval.

The survey of 957 likely voters, conducted between 18 October and 22 October, has a credibility interval of 3.6 percentage points.