WASHINGTON - US Republican Mitt Romney has pulled ahead of US President Barack Obama for the first time in more than a month and leads 45 percent to 44 percent among likely voters, according to a Reuters/Ipsos tracking poll released on Wednesday.

With under four weeks until the November 6 election, Obama's post-convention bounce in polls has now disappeared. Voters warmed to Romney across a range of policy issues following a strong debate performance by the Republican last week.

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On Tuesday, the tracking poll had the two candidates tied at 45 percent.

The online survey of 1,027 likely voters was conducted between October 6 and October 10. The precision of the poll is measured using a credibility interval, which is plus or minus 3.5 percentage points for likely voters.