Hillary Clinton and her aides have refused to be served with legal papers in a defamation dispute with Tulsi Gabbard, it has been claimed.

Gabbard's lawyers say they were turned away by the Secret Service and later by Clinton's attorney when they tried to deliver the paperwork.

The Democratic presidential hopeful is suing Clinton for $50million over an interview last year in which the 2016 nominee suggested that Gabbard was the 'favorite of the Russians'.

Gabbard's attorney Brian Dunne told the New York Post that Clinton was 'so intimidated by Tulsi Gabbard that she won't accept service of process'.

Democratic presidential hopeful Tulsi Gabbard (pictured on the debate stage in Atlanta last November) is suing Hillary Clinton for $50million

Dunne, the attorney, said Gabbard's representatives had tried to deliver the papers in person at the Clinton residence in Chappaqua, New York.

However, they were allegedly turned away by Secret Service agents who protect the home.

Gabbard's camp says the agents directed them to Clinton's lawyer David Kendall, who said he could not accept the papers on her behalf.

Dunne said Gabbard's team was now considering its next move.

Gabbard filed the lawsuit in federal court in Manhattan last week, accusing Clinton of promoting 'extremely dubious conspiracy theories'.

The lawsuit alleges that Clinton 'harmed her political and personal rival's reputation and ongoing presidential campaign'.

The former Secretary of State is also accused of starting a 'damaging whisper campaign based on baseless, but vicious, untruths'.

Gabbard's lawyers claim that Clinton holds a 'special hatred and animosity for Tulsi' for backing Bernie Sanders in the 2016 primary campaign.

Clinton spokesman Nick Merrill last week described the lawsuit as 'ridiculous'.

Former Secretary of State Hillary Clinton (pictured in California earlier this month) suggested that Tulsi Gabbard was a 'favorite of the Russians'

As a public figure, Gabbard must show that the defendant acted with actual malice to recover damages from Clinton.

In addition, US courts have said in the past that 'rhetorical hyperbole' associated with politics is constitutionally protected speech.

The row turns on a podcast last year in which Clinton suggested to former Obama aide David Plouffe that Gabbard was the 'favorite of the Russians'.

'She's the favorite of the Russians, they have a bunch of sites and bots and other ways of supporting her so far,' Clinton said.

Clinton did not name Gabbard, but there have been no claims of Russian backing for any other female Democrat in the race.

Her spokesman Merrill later indicated that Gabbard was the candidate she had in mind, saying: 'If the nesting doll fits'.

Gabbard retorted by calling Clinton 'the queen of warmongers... and personification of the rot that has sickened the Democratic Party for so long.'

The 38-year-old has long been regarded as an outlier in the Democratic party and raised eyebrows by visiting Syria's president Bashar al-Assad in 2017.

She also questioned whether Assad was behind a chemical weapons attack which killed dozens in Syria the same year, as intelligence services believe.

Gabbard also voted 'present' on the two articles of impeachment against Donald Trump, saying he was 'guilty of wrongdoing' but should not be removed from office.