maria chapelle-nadal
Maria Chappelle-Nadal has refused to resign over her comments screengrab/YouTube

A US state senator from Missouri is being investigated by the Secret Service and facing calls to resign after saying she hopes Donald Trump gets assassinated.

Democratic state senator Maria Chappelle-Nadal wrote the message, "I hope Trump is assassinated!" in reply to a Facebook post, before later deleting it.

She said she made the incendiary post in relation to events in Charlottesville, Virginia over the weekend, which saw a demonstration involving white supremacists marred by violence and President Trump condemned for his response.

The Secret Service confirmed it was "looking into the comments" made by Chappelle-Nadal, saying "all threats against the President" will be investigated.

The senator dismissed calls from other politicians, including some within her own party, to resign.

She told the St Louis Post-Dispatch: "I didn't mean what I put up. Absolutely not. I was very frustrated. Things have got to change.

"It was in response to the concerns that I am hearing from residents of St. Louis. I have deleted it, and it should have been deleted, but there is something way more important that we should be talking about."

She added: "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."

Chappelle-Nadal went on to say that the assassination comments were in response to events in Charlottesville, which saw a demonstration involving white supremacists turn violent when a participant allegedly drove into a crowd of counter-protesters, killing a 32-year-old woman and injuring 20 others.

Trump was condemned by figures from both major US political parties for his response to the violence. They accused the President of suggesting there was moral equivalence between the two sides of demonstrators.

"There are people who are afraid of white supremacists," Chappelle-Nadal said.

"There are people who are having nightmares. There are people who are afraid of going out in the streets. It's worse than even Ferguson."

But the leader of the Democratic Caucus in the Missouri senate, Gina Walsh, said her colleague "should be ashamed of herself for adding her voice to this toxic environment."

Democratic Senator Claire McCaskill, also of Missouri, said: "I condemn it. It's outrageous. And she should resign."

The Republican Governor of Missouri, Eric Greitens, has also called for her to quit her post.

He said: "We can have differences in our country, but no one should encourage political violence. The senator should resign."