Former Secretary of State Hillary Clinton, accompanied by her daughter Chelsea Clinton, former Congresswoman Gabby Giffords, and Mark Kelly, speaking to Iowa voters at Iowa State University in Ames, Iowa on Saturday, January 30, 2016. (Photo by Melina Mara/The Washington Post)

DES MOINES, Iowa - Hillary Clinton and Bernie Sanders are locked in a statistical tie in the hard-fought and unexpectedly close Iowa Democratic presidential contest, a new Des Moines Register-Bloomberg poll found Saturday.

The respected survey found Clinton commands 45 percent of Democratic support and Sanders 42 percent. The poll of 602 likely Democratic caucus-goers has a margin of error of 4 percentage points, meaning Clinton's lead is within the margin of error. The survey comes three days before the first presidential voting of 2016 and reflects a late surge by Sanders, an independent senator from Vermont who was once considered a long shot here.

With Democratic candidates Hillary Clinton and Bernie Sanders virtually tied ahead of Monday's caucus, things are heating up on the ground in the Hawkeye State. Both candidates made a splash with large rallies over the weekend, but behind the scenes is where the real action is taking place. (Alice Li,Dalton Bennett/The Washington Post)

Other Iowa polls over the past two weeks have had Clinton ahead by an average of 3.4 points according to Real Clear Politics tabulations. Most of those polls also have margins of error that put Clinton's lead in some doubt. The Register poll, conducted by pollster Ann Selzer, has a record of accuracy and is often considered the state gold standard.

Clinton had held a steady lead in Iowa for months until Sanders closed on her in December and January. He was even with Clinton or ahead of her in some polls earlier this month, which rattled the Clinton campaign and raised ghosts of her crushing Iowa loss to insurgent candidate Barack Obama in 2008.

The Sanders campaign claimed the poll shows momentum on its side.

“Our campaign has come a very long way in eight months. In late May, according to the Register/Bloomberg poll, we were down by 41 points. Today we are virtually tied,” said Jeff Weaver, Sanders’ campaign manager.

The campaign noted that the same poll showed Clinton with a formidable 41-point lead last spring, when both Clinton and Sanders entered the race.