FILE PHOTO: Democratic 2020 U.S. presidential candidates Senator Elizabeth Warren (D-MA) and Senator Bernie Sanders (I-VT) are seen on television monitors in the press room at the seventh Democratic 2020 presidential debate at Drake University in Des Moines, Iowa, U.S., January 14, 2020. REUTERS/Brenna Norman

WASHINGTON (Reuters) - Senator Bernie Sanders is leading other Democratic presidential candidates with 25% of the likely vote in Iowa, just over a week before statewide caucuses in the state, a New York Times/Siena College poll released Saturday showed.

Sanders has gained six points since the last Times/Siena poll in October, while support for Pete Buttigieg, the former mayor of South Bend, Indiana, and former Vice President Joe Biden has remained steady at 18% and 17%, respectively, it showed. He is also leading some other opinion polls in the state.

Sanders’ gains come at the expense of his fellow progressive, Senator Elizabeth Warren of Massachusetts, whose support dropped to 15% from 22% in the October poll, the New York Times reported.

Iowa voters cast ballots in Feb. 3 party caucuses in the first contest in the state-by-state process of selecting a Democratic challenger to Republican President Donald Trump in the Nov. 3 general election. Thirteen Democrats are in the race.

Sanders’s gains came after a weeks-long controversy over whether he told Warren in a 2018 meeting that a woman could not beat Trump, a charge he has denied.

The Vermont senator this week scrapped three scheduled Iowa campaign appearances to remain in Washington for Trump’s impeachment trial, along with three other Democratic senators running for president.

Trump, a Republican, is charged by the Democratic-controlled House of Representatives with abusing the powers of his office when he asked Ukraine to investigate Biden, and obstructing a congressional inquiry into his conduct.

The Times/Siena survey of 1,689 registered voters in Iowa was conducted from Jan. 20 to Jan. 23, and has a margin of error of plus or minus 4.8 percentage points.