WASHINGTON, Sept. 26 (Xinhua) — The U.S. public's intent to vote for president has declined sharply to 69 percent, down by 7 percentage points from 2012, a Gallup poll found Monday.

The poll was released just ahead of this year's first presidential debate held in the night between Republican candidate Donald Trump and his Democratic rival Hillary Clinton, both of whom have low favorable ratings among U.S. voters.

The Sept. 14-18 poll found that 72 percent of Americans had given a lot of thought to this year's presidential election, down 2 percentage points from 2012. This is the lowest figure since 2000.

Sharp differences exist among different age groups in terms of the intent to vote in this year's presidential election, the poll found.

Among American adults aged 18 to 34, only 47 percent said they would definitely vote, down sharply from 58 percent in 2012.

Among the adults aged 35 to 54, 72 percent said they would definitely vote, down from 79 percent in 2012. Among those aged 55 above, 82 percent would definitely vote, down only 1 percentage point from 2012.

"While Americans are giving a similar level of thought to the presidential election compared with previous years, the percentage saying they are certain they will vote is lagging, particularly among young adults," Gallup said.

The decline in young Americans' intent to vote likely reflects the persistently poor images of both major party nominees, as well as Clinton's difficulty in winning over the young adults who are much more favorable toward Bernie Sanders, Clinton's Democratic rival in the nomination race, Gallup said.