NEW YORK/WASHINGTON, June 8 (Reuters) - U.S. Senator Elizabeth Warren will soon endorse presumptive Democratic presidential nominee Hillary Clinton and, while not currently interested in serving as her running mate, has not ruled it out, several sources close to Warren told Reuters.

Advisers to Warren, a fiery critic of Wall Street and a popular figure among progressive Democrats, have been in close contact with Clinton's campaign team and the conversations have increased in frequency in recent weeks, the sources said.

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Warren, 66, represents her home state of Massachusetts in the U.S. Senate. The sources said that foremost in her thinking is how best to help the Democratic Party defeat the presumptive Republican nominee Donald Trump in the Nov. 8 presidential election and advance issues such as income inequality which top Warren's agenda.

An endorsement of Clinton could come within a week or two, one of the sources said. Clinton has been appealing for Democratic Party unity. On Twitter over the weekend, Warren echoed that call and emphasized the importance of the party coming together to beat Trump.

"Get ready, Donald," she tweeted. "We're coming."

See Elizabeth Warren through the years:



22 PHOTOS Sen. Elizabeth Warren See Gallery US Senator Warren to endorse Clinton, sources say Sen. Elizabeth Warren, D-Mass., attends a Senate Armed Services Committee hearing in Dirksen Building titled 'Foreign Cyber Threats to the United States,' featuring testimony by Director of National Intelligence James Clapper and others, January 5, 2016. (Photo By Tom Williams/CQ Roll Call) Senate Armed Services Committee members (L-R) Sen. Martin Heinrich (D - NM), Sen. Elizabeth Warren (D-MA) and Sen. Gary Peters (D-MI) talk during a hearing in the Dirksen Senate Office Building on Capitol Hill January 5, 2017 in Washington, DC. The intelligence chiefs testified to the committee about cyber threats to the United States and fielded questions about effects of Russian government hacking on the 2016 presidential election. (Photo by Chip Somodevilla/Getty Images) Senate Armed Services Committee Chairman John McCain (R-AZ) (L) and Sen. Elizabeth Warren (D-MA) arrive for a hearing with the Director of National Intelligence and National Security Agency chief in the Dirksen Senate Office Building on Capitol Hill January 5, 2017 in Washington, DC. The intelligence chiefs testified to the committee about cyber threats to the United States and fielded questions about effects of Russian government hacking on the 2016 presidential election. (Photo by Chip Somodevilla/Getty Images) Democratic Nominee for President of the United States former Secretary of State Hillary Clinton, accompanied by Senator Elizabeth Warren (D-MA), speaks to and meets New England voters during a rally at Saint Anselm College in Manchester, New Hampshire on Monday October 24, 2016. (Photo by Melina Mara/The Washington Post via Getty Images) Mark Wahlberg, Former Boston Police Commissioner Ed Davis, Boston Police Commissioner Billy Evans, Former Boston Red Sox player David Ortiz, Dun 'Danny' Meng, Jessica Downes, Patrick Downes, Senator Elizabeth Warren, director Peter Berg and Harvard Law professor Bruce Mann pose on the red carpet at the 'Patriots Day' screening at the Boch Center Wang Theatre on December 14, 2016 in Boston, Massachusetts. (Photo by Natasha Moustache/WireImage) Democratic Nominee for President of the United States former Secretary of State Hillary Clinton, accompanied by Senator Elizabeth Warren (D-MA), speaks to and meets New England voters during a rally at Saint Anselm College in Manchester, New Hampshire on Monday October 24, 2016. (Photo by Melina Mara/The Washington Post via Getty Images) Former Red Sox player David Ortiz talks with Senator Elizabeth Warren at the 'Patriots Day' screening at the Boch Center Wang Theatre on December 14, 2016 in Boston, Massachusetts. (Photo by Natasha Moustache/WireImage) Democratic presidential nominee Hillary Clinton and Senator Elizabeth Warren hold a rally at St. Anselm College in Manchester, NH on Oct. 24, 2016. (Photo by Suzanne Kreiter/The Boston Globe via Getty Images) U.S. Senator Elizabeth Warren speaks at a Manchester 'New Hampshire Together' Canvass Launch event in Manchester, NH on Sept. 24, 2016. (Photo by Craig F. Walker/The Boston Globe via Getty Images) Senior United States Senator from Massachusetts, Elizabeth Warren speaks onstage at EMILY's List Breaking Through 2016 at the Democratic National Convention at Kimmel Center for the Performing Arts on July 27, 2016 in Philadelphia, Pennsylvania. (Photo by Paul Zimmerman/Getty Images For EMILY's List) US Senator Elizabeth Warren, Democrat of Massachusetts, holds up copies of Wells Fargo earnings call transcripts as she questions John Stumpf, chairman and CEO of Wells Fargo, as he testifies about the unauthorized opening of accounts by Wells Fargo during a Senate Banking, Housing and Urban Affairs Committee hearing on Capitol Hill in Washington, DC, September 20, 2016. (SAUL LOEB/AFP/Getty Images) Sen. Elizabeth Warren (D-MA) along with members of the Democratic Women of the Senate acknowledge the crowd on the fourth day of the Democratic National Convention at the Wells Fargo Center, July 28, 2016 in Philadelphia, Pennsylvania. Democratic presidential candidate Hillary Clinton received the number of votes needed to secure the party's nomination. An estimated 50,000 people are expected in Philadelphia, including hundreds of protesters and members of the media. The four-day Democratic National Convention kicked off July 25. (Photo by Jessica Kourkounis/Getty Images) Sen. Elizabeth Warren (D-MA) delivers remarks on the first day of the Democratic National Convention at the Wells Fargo Center, July 25, 2016 in Philadelphia, Pennsylvania. An estimated 50,000 people are expected in Philadelphia, including hundreds of protesters and members of the media. The four-day Democratic National Convention kicked off July 25. (Photo by Alex Wong/Getty Images) Representative Joseph P. Kennedy III welcomes Massachusetts Senator Elizabeth Warren on stage on Day 1 of the Democratic National Convention at the Wells Fargo Center in Philadelphia, Pennsylvania, July 25, 2016. (BRENDAN SMIALOWSKI/AFP/Getty Images) Former Secretary of State Hillary Clinton accompanied by Senator Elizabeth Warren (D-MA) speaks to and meets Ohio voters during a rally at the Cincinnati Museum Center at Union Terminal in Cincinnati, Ohio on Monday, June 27, 2016. (Photo by Melina Mara/The Washington Post via Getty Images) The Late Show with Stephen Colbert airing live, Thursday July 21, 2016 in New York. With guest Elizabeth Warren . (Photo by Scott Kowalchyk/CBS via Getty Images) Sen. Elizabeth Warren (D-MA) arrives in the Capitol for the on Tuesday, June 28, 2016. (Photo By Bill Clark/CQ Roll Call) U.S. Sen. Elizabeth Warren (D-MA) (R) meets with Supreme Court nominee Merrick Garland (L), chief judge of the D.C. Circuit Court, April 14, 2016 on Capitol Hill in Washington, DC. Garland continued to place visits to Senate members after he was nominated by President Barack Obama to succeed the late Justice Antonin Scalia. (Photo by Alex Wong/Getty Images) Senator Elizabeth Warren, a Democrat from Massachusetts, listens as Janet Yellen, chair of the U.S. Federal Reserve, testifies during a Senate Banking Committee hearing in Washington, D.C., U.S., on Tuesday, June 21, 2016. Yellen offered a subtle change to her outlook from less than a week ago, saying she and her colleagues were on watch for whether, rather than when, the U.S. economy would show clear signs of improvement. (Photographer: Pete Marovich/Bloomberg via Getty Images) Sen. Elizabeth Warren, D-Mass., greets guests during a rally on the east lawn of the Capitol to urge Senate Minority Leader Mitch McConnell, R-Ky., to hold a vote on the 'Seniors and Veterans Emergency Benefits Act,' March 9, 2016. The legislation would provide a one time payment to seniors, veterans and other SSI recipients who will not get a cost-of-living adjustment this year. (Photo By Tom Williams/CQ Roll Call) Senators Bob Corker (L) and Elizabeth Warren (R) speak before a Senate Banking Committee on the semiannual monetary report to Congress hearing in Washington, USA on February 11, 2016. (Photo by Samuel Corum/Anadolu Agency/Getty Images) Senator Elizabeth Warren (D-MA), talks with Rep. Elijah Cummings (D-MD) in the House chamber prior to President Obama's State of the Union speech on Capitol Hill in Washington, February 12, 2013. (REUTERS/Charles Dharapak/Pool) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Warren has stayed neutral in the Democratic primary race, notably remaining the only woman senator not throwing her support behind the first woman presidential nominee of a major political party.

Were she to join the Clinton ticket, she could help energize progressives and win over supporters of Clinton's rival Bernie Sanders, a democratic socialist U.S. senator from Vermont. Sanders' calls for reining in Wall Street and breaking up big banks dovetail with Warren's views.

Warren, a former special adviser in the Obama administration for the Consumer Financial Protection Bureau, has been one of the Democrats' most effective Trump critics.

An ongoing feud with Trump gained steam on social media with a series of posts in which she labeled the celebrity businessman racist, sexist and xenophobic and said she was going to fight to make sure his "toxic stew of hatred and insecurity never reaches the White House."

Warren joined Clinton late last month in criticizing Trump for rooting for the 2008 financial crisis and delivered a 10-minute invective on the subject at an annual Washington gala two weeks ago.

"What kind of a man roots for people to get thrown out of their house? I'll tell you exactly what kind of man does that," Warren said. "It is a man who cares about no one but himself - a small insecure money-grubber who doesn't care who gets hurt so long as he makes a profit off it."

Trump has ridiculed Warren by calling her Pocahontas in a mocking reference to her having said in the past that she had Native American ancestry. Pocahontas was a famous Native American in early colonial Virginia.

(Additional reporting by Megan Cassella and Amanda Becker in Washington; Editing by Amran Abocar and Howard Goller)

See some of Clinton's potential running mates:



11 PHOTOS Hillary Clinton potential running mates, VPs See Gallery US Senator Warren to endorse Clinton, sources say Tim Kaine The junior Democratic Senator from the swing state of Virginia could be a strategic selection for Hillary. Kaine also served as the governor of Virginia from 2006- 2010. The junior Democratic Senator from the swing state of Virginia could be a strategic selection for Hillary. Kaine also served as the governor of Virginia from 2006- 2010. (Photo by Samuel Corum/Anadolu Agency/Getty Images) Elizabeth Warren The current U.S. Senator from Massachusetts is popular among progressive Democrats, and some even tried to draft her to run for president herself in 2016. (Photo by Andrew Harrer/Bloomberg via Getty Images) Sherrod Brown Insiders believe that the senior U.S. Senator from Ohio could help Clinton increase her popularity with working-class voters, a group she has yet to win in a big way so far in primary contests. (Photo By Bill Clark/CQ Roll Call) Cory Booker The U.S. Senator from New Jersey is both youthful and charismatic and would add racial diversity to a Clinton ticket. (Photo by KK Ottesen for The Washington Post via Getty Images) Tom Perez The current U.S. Secretary of Labor is considered a sleeper pick by many Democrats because he is not well known outside of D.C., but some believe his strength and popularity among union workers and other progressive groups could be an asset to Clinton's ticket. (Photo By Tom Williams/CQ Roll Call) Bernie Sanders The Independent from Vermont has become Hillary Clinton's primary rival for the Democratic nomination, garnering a surprising amount of support. Bringing Sanders onto the ticket could help to unite both sets of supporters who have been split in Democratic primaries. (Photo by Ralph Freso/Getty Images) Martin O'Malley A former 2016 rival of Hillary Clinton, and former Maryland governor, Martin O’Malley could help bring some executive experience, along with a slight youthful boost to the ticket. (Photo by Joe Raedle/Getty Images) Tom Vilsack The Secretary of Agriculture since 2009, Tom Vilsack also served as the governor of Iowa from 1999 to 2007. Vilsack could bring some governing experience along with swing state influence. (BELGIUM - Tags: AGRICULTURE POLITICS BUSINESS) Evan Bayh Evan Bayh could bring a more right leaning brand of politics to the ticket. Bayh previously served as the junior U.S. Senator from Indiana from 1999 to 2011, and also as the 46th Governor of Indiana from 1989 to 1997. Joe Biden While the likelihood of him agreeing to take on the veep job again might be low, Biden's popularity among Democrats would likely boost Clinton's chances. (Photo credit MANDEL NGAN/AFP/Getty Images) Bill Clinton Hillary's husband is technically allowed to serve in the job, and some legal experts even think he'd be able to take office if necessary. Unfortunately for the diehard Clinton supporters, a Clinton-Clinton ticket will probably be a dream that never comes true. (Photo By Bill Clark/CQ Roll Call) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

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