A US state senator is being investigated by the Secret Service for saying she hopes President Donald Trump will be assassinated.

Maria Chappelle-Nadal, a Democrat state senator from Missouri, made the remarks on her personal Facebook page but then later deleted them.

The politician said “I hope Trump is assassinated!” in response to a post suggesting Vice President Mike Pence would try to oust Mr Trump from the Oval Office.

The Secret Service said they are “looking into the comments” and say “all threats against the President” will be subject to investigation.

Ms Chappelle-Nadal, who gained prominence for criticising the Ferguson police shooting of Michael Brown in 2014, has since deleted the comment and apologised.

But the politician, who has been an outspoken activist while in the Legislature, has been insistent she will not be stepping down over the furore and said her comment was borne out of frustration with the current political landscape.

She also said she was frustrated with the president’s response to the white supremacist rally in Charlottesville.

Violence on the streets of Charlottesville Show all 9 1 /9 Violence on the streets of Charlottesville Violence on the streets of Charlottesville Protesters clash and several are injured White nationalist demonstrators clash with counter demonstrators at the entrance to Lee Park in Charlottesville, Virginia. A state of emergency is declared, August 12 2017 Violence on the streets of Charlottesville Trump supporters at the protest A white nationalist demonstrator walks into Lee Park in Charlottesville, Va., Saturday, Aug. 12, 2017. Hundreds of people chanted, threw punches, hurled water bottles and unleashed chemical sprays on each other Saturday after violence erupted at a white nationalist rally in Virginia. AP Photo Violence on the streets of Charlottesville State police stand ready in riot gear Virginia State Police cordon off an area around the site where a car ran into a group of protesters after a white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville Militia armed with assault rifles White nationalists, neo-Nazis and members of the 'alt-right' with body armor and combat weapons evacuate comrades who were pepper sprayed after the 'Unite the Right' rally was declared a unlawful gathering by Virginia State Police. Militia members marched through the city earlier in the day, armed with assault rifles. Getty Images Violence on the streets of Charlottesville Statue of Confederate General Robert E Lee The statue of Confederate General Robert E. Lee stands behind a crowd of hundreds of white nationalists, neo-Nazis and members of the 'alt-right' during the 'Unite the Right' rally 12 August 2017 in Charlottesville, Virginia. They are protesting the removal of the statue from Emancipation Park in the city. Getty Images Violence on the streets of Charlottesville Racial tensions sparked the violence White nationalists, neo-Nazis and members of the 'alt-right' exchange insults with counter-protesters as they attempt to guard the entrance to Lee Park during the 'Unite the Right' rally Getty Violence on the streets of Charlottesville A car plows through protesters A vehicle drives into a group of protesters demonstrating against a white nationalist rally in Charlottesville, Virginia. The incident resulted in multiple injuries, some life-threatening, and one death. AP Photo Violence on the streets of Charlottesville Rescue personnel help injured people after a car ran into a large group of protesters after an white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville President Donald Trump speaks about the ongoing situation in Charlottesville, Virginia from his golf club in Bedminster, New Jersey. He spoke about "loyalty" and "healing wounds" left by decades of racism.

“I am not resigning. When people of colour are respected by this White House and they are willing to do real work, I'll sit down with them. People are traumatized!” she said on Twitter.

She told the St Louis Post-Dispatch: "I didn't mean what I put up. Absolutely not. I have deleted it, and it should have been deleted.

"I am not resigning. What I said was wrong, but I am not going to stop talking about what led to that, which is the frustration and anger that many people across America are feeling right now."

The comments about assassination have drawn swift condemnation from Republicans and fellow democrats and some have called for her to step down,

Stephen Webber, the chairman of the Missouri Democratic Party, said the remarks were “indefensible” and the party “will absolutely not tolerate calls for the assassination of the president.”

Democrat Senator Claire McCaskill said: “I condemn it. It’s outrageous and she should resign.”

Ms Chappelle-Nadal, who has been subject to frequent vitriolic abuse from Trump supporters online, became a leading critic during the protests in Ferguson, Missouri after the police killing of Michael Brown, an 18-year-old black resident who was unarmed when fatally shot by an officer in 2014.

The politician, who is from the St. Louis suburb of University City, took part in protests against the fatal shooting and was among the protesters who were tear-gassed by law enforcement officials.

She argued institutional inequality was a critical issue which lay behind the civil unrest in Ferguson and had contributed to heightened tensions between police and the community, saying: "I have to tell you that there has been systematic racism, institutionally in state government for decades, including my own state party,” she said. “People are angry, and they are hurt, and they’re trying to figure out: how are they going to receive justice?”

Johnny Depp was also recently forced to apologise for joking about assassinating President Trump, saying his remarks were in “poor taste.”

Speaking during an appearance at Glastonbury music festival, the Pirates of the Caribbean actor publicly pondered how long it had been since an actor had killed a US president.

"I apologise for the bad joke I attempted last night in poor taste about President Trump," Depp said in a statement.