By Chris Kahn

NEW YORK (Reuters) - Republican presidential candidate Donald Trump narrowed his deficit to Democratic rival Hillary Clinton to 7 percentage points from 15 points late last week, according to a Reuters/Ipsos poll released on Tuesday,

Polling was under way on Tuesday at the Republican National Convention in Cleveland to officially nominate Trump as the party's candidate for the Nov. 8 presidential election. Clinton is due to be officially nominated at the Democratic convention in Philadelphia next week.

Forty-three percent of likely voters supported Clinton in the July 15-19 poll, while 36 percent supported Trump. The poll included 1,069 voters and had a credibility interval, a measure of accuracy, of 3 percentage points.

The previous poll, in which Trump trailed Clinton by 15 percentage points, covered the five-day period that ended July 14.

Trump's rise appeared partly fueled by a decline in the number of voters who remained on the sidelines. The percentage of voters who supported neither candidate dropped to 12 percent in the July 15-19 poll from 15 percent in the July 10-14 poll.

Clinton has led in the poll most of the year.

The last time that Trump matched Clinton's level of support was in mid-May, after his remaining rivals for the Republican nomination dropped out and many Republican leaders started to openly support his bid for the White House.

This week's Republican convention provides another opportunity for party leaders to publicly embrace Trump's campaign.

Presidential nominees typically see a boost in voter support following their party conventions. In 2012, Republican nominee Mitt Romney jumped by about 5 percentage points in the Reuters/Ipsos poll following the Republican convention.

This year, however, Republican leaders have struggled to give a full-throated endorsement of Trump's "America First" campaign over his hard line on immigration and trade, and his fiery rhetoric that some have called bigoted.

Many Republican elders, including both former presidents Bush and the last two presidential nominees, Romney and John McCain, are staying away from Cleveland.

The convention also has been marred by protests from anti-Trump delegates and a controversy over a speech by Trump's wife, Melania, that included a section that was strikingly similar to a portion of the speech given by Michelle Obama at the Democratic convention in 2008 when her husband, Barack Obama, was seeking his first term as president.

(Editing by Richard Valdmanis and Leslie Adler)