WASHINGTON - Republican challenger Mitt Romney has extended his lead over US President Barack Obama to 3 percentage points, according to a Reuters/Ipsos tracking poll released on Thursday, ahead of a high-stakes debate between the two candidates' running mates.

Romney now leads the Democrat by 47 percent to 44 percent among likely voters in the online poll, with less than a month before the Nov. 6 election. The Reuters/Ipsos tracking poll released on Wednesday had shown Romney with a one-point lead over Obama, his first lead in the survey in more than a month.

Romney has been enjoying one of his best runs of the campaign after handily winning the first presidential debate last week, partially due to Obama's passive performance in that contest.