Democratic presidential hopeful Hillary Clinton extended her lead over Republican rival Donald Trump to 13 percentage points in a Reuters/Ipsos opinion poll released on Tuesday, up from 10 points at the end of last week.
The July 8-12 poll showed 46 percent of likely voters supported Clinton, the former secretary of state, while 33 percent supported Trump, a celebrity real estate developer. Another 21 percent did not support either candidate.
That compared with 45 percent who supported Clinton and 35 percent who supported Trump in the five days to July 8.
Clinton, the presumptive Democratic nominee, has mostly led in the national online poll this year. The last time Trump came close to Clinton's popularity was in early May, when his last two rivals for the Republican nomination dropped out of the race and party leaders started to line up behind his campaign.
Trump, who is expected to become the official Republican nominee at the party's convention next week, has since lost ground in the poll as he struggled to refocus his campaign from the Republican nominating contests to the Nov. 8 general election.
Over the past several weeks, Trump has faced criticism for his past business dealings and has quarreled with Republican leaders over his rejection of international trade agreements and his promises to crack down on immigration.
Clinton, meanwhile, has been dogged by criticisms of how she handled classified information as secretary of state.
James Comey, director of the Federal Bureau of Investigation, said last week that Clinton and her staff were "extremely careless" with sensitive information but recommended that the government not seek criminal charges against her.
Still, Americans have become increasingly positive about Clinton this month, with half of likely voters now saying they have a favorable view of her, according to the poll, up from 46 percent on July 1.
Some 60 percent of likely voters have an unfavorable view of Trump, compared with 58 percent on July 1.
The Reuters/Ipsos poll surveyed 1,146 likely voters across the continental United States, Alaska and Hawaii. It has a credibility interval, a measure of accuracy, of 3 percentage points.