Tulsi Gabbard, a Democrat member of US Congress, has announced that she is running for president in 2020.

Gabbard, a delegate for Hawaii in the House of Representatives, told CNN in an interview set to air on Saturday night that she will formally announce her candidacy the next week.

"There are a lot of reasons for me to make this decision," Gabbard told the broadcaster. "There are a lot of challenges that are facing the American people that I'm concerned about and that I want to help solve."

The 37-year-old Iraq War veteran is the first Hindu elected to Congress and the first member born in the US territory of American Samoa.

Gabbard is joining what is expected to be a crowded Democratic field. Senator Elizabeth Warren of Massachusetts has already formed an exploratory committee and is moving quickly with trips across early primary states.

California Senator Kamala Harris, New Jersey Senator Cory Booker and Vermont Senator Bernie Sanders are weighing their own presidential bids and are expected to announce decisions in the coming weeks.

Former Obama administration housing chief Julian Castro is also expected to announce his candidacy on Saturday.

Gabbard said although her "main issue" will be "war and peace", she will push for combating climate change, reforming the criminal justice system and providing healthcare for all Americans.

Secret meeting with Syria's Assad

Gabbard's run would not be without controversy. In 2016, she alarmed fellow Democrats when she met Donald Trump during his transition to the presidency.

She also met Syrian President Bashar al-Assad, a meeting she claimed was "important" to "achieve peace" for the Syrian people.

Assad is accused of war crimes, including the killing of hundreds of thousands of Syrians. Gabbard has questioned whether the Syrian leader was actually responsible for a chemical attack on civilians that killed dozens and led to a retaliatory US attack on a Syrian airbase.

Minutes after Gabbard's announcement, Republicans released a "cheat sheet" about the Hawaii congresswoman dubbing her "Assad's mouthpiece in Washington".

Gabbard backed Bernie Sanders over Hillary Clinton in the 2016 Democratic presidential primary, even resigning her position as a vice chairwoman of the Democratic National Committee to express her support.

Asked last year whether she would still consider running if Sanders ran, Gabbard said Sanders is a friend and she didn't know what his plans were.

"I'm thinking through how I can best be of service and I'll make my decision based on that," she said.