WASHINGTON - US Vice President Joe Biden has held a surprise meeting with senior Democratic Senator Elizabeth Warren in Washington as he appears to be getting serious to challenge Hillary Clinton for the Democratic nomination for president, reports say. 

The unscheduled meeting with Warren, an influential Democrat who has been under pressure to run for the White House, took place at the Naval Observatory, the vice president's official residence, on Saturday, according to The Washington Post.

An Obama administration official stated Biden left his family home in the state of Delaware at the last minute to travel Washington for a private meeting will return home the same day.

Both of the officials revealed the information while speaking on condition of anonymity because they weren't allowed to discuss the development publicly.

Meanwhile, two sources told CNN that the two politicians held a face-to-face meeting, the latest sign that the vice president is seriously considering entering the 2016 race.

Ms. Warren, a vocal advocate for Wall Street reform, has not endorsed Hillary Clinton, Senator Bernie Sanders or the other Democratic candidates.

A rising star in the party, Warren has given no indication she’s interested in entering the 2016 race. However, she has been reportedly laying the groundwork for a potential Biden candidacy.

Biden has been in contact with longtime aides and donors who could help finance a viable presidential campaign against well-funded candidates in the 2016 race.

Although Biden has not made up his mind yet, his advisers said the vice president and his aides have begun working out issues like fundraising and an early primary state strategy, according to an AP report.

At his family home in Delaware, Biden has huddled with longtime confidantes, Mike Donilon, a lawyer and political campaign consultant, and former Senator Ted Kaufman, as well as with his grandson, Hunter Biden, and his sister, Valerie Owens Biden, who has played a key role in all his previous campaigns.

The team has settled on a one-month window starting from September 1, in which Biden could potentially announce plans to run for president, according to AP.Advisers say that if Biden does not enter the race by October 1, it might be too late for him to get the petition signatures and delegates lined up for the ballot in early primary states.

According to a New York Times column by veteran journalist Maureen Dowd published earlier this month, when Biden’s son, Beau, realized that he would not survive brain cancer, he talked to his father and urged him to challenge Clinton.

According to Dowd, the ailing son argued that Biden would be a better president than Clinton.

Dowd wrote that the vice president is “talking to friends, family and donors about jumping in” following his son’s passing.

Following the death of Beau, supporters offered condolences to Biden and called on him to run for president.

Seventeen Republicans are seeking their party’s nomination for president but only a few are considered serious contenders.

Democrat front-runner Clinton is competing against only three Democrats and one independent senator, Bernie Sanders, for the Democratic Party's nomination.

Only Sanders is considered at all competitive in the early primaries, even as he operates with far less money than the former secretary of state.

Donald Trump, the current leading candidate for the Republican nomination, says it would be tougher to beat Biden if he comes up after defeating Clinton in Democratic primaries.

“Her numbers are going down drastically, so somebody like Biden could probably go in and do very well and maybe win,” he said.“I actually think Hillary will be easy if it’s her,” Trump said. “But I’m not so sure it’s going to be her.”