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.

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.

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