U.S. House Speaker Nancy Pelosi announced Sunday that she has taken steps to ensure the safety of Rep. Ilhan Omar following President Donald Trump's retweet of a video that purports to show the Minnesota Democrat being dismissive of the Sept. 11 terrorist attacks.

The California Democrat also called on Trump to take down the video. Soon after her public request, the video disappeared as a pinned tweet at the top of Trump's Twitter feed, but it was not deleted.

Pelosi was among Democrats who had criticized Trump over the tweet, with some accusing him of trying to incite violence against the Muslim lawmaker who has already seen one upstate New York man face criminal charges for making death threats against her.

Omar said she's faced increased death threats since Trump retweeted the video. "Violent crimes and other acts of hate by right-wing extremists and white nationalists are on the rise in this country and around the world," she said. "We can no longer ignore that they are being encouraged by the occupant of the highest office in the land."

"We are all Americans."

The White House defended Trump earlier Sunday, saying the president has a duty to highlight Omar's history of making comments that others find offensive and that he wished no "ill will" upon the first-term lawmaker.

On Monday, however, Trump singled out both Omar and Pelosi on Twitter, accusing the representative of controlling the speaker.

Before Nancy, who has lost all control of Congress and is getting nothing done, decides to defend her leader, Rep. Omar, she should look at the anti-Semitic, anti-Israel and ungrateful U.S. HATE statements Omar has made. She is out of control, except for her control of Nancy! —@realDonaldTrump

Pelosi, who was travelling in London, issued a statement saying she had spoken with congressional authorities after Trump's tweet "to ensure that Capitol Police are conducting a security assessment to safeguard Congresswoman Omar, her family and her staff."

"They will continue to monitor and address the threats she faces," the speaker said. She called on Trump to discourage such behaviour.

"The president's words weigh a ton, and his hateful and inflammatory rhetoric creates real danger," Pelosi said. "President Trump must take down his disrespectful and dangerous video."

News footage of 9/11

The video in Trump's initial tweet included a snippet from a recent speech Omar gave to the Council on American-Islamic Relations, in which she described the 2001 terrorist attack on the World Trade Center as "some people did something," along with news footage of the hijacked airplanes hitting the Twin Towers. Trump captioned his tweet with: "WE WILL NEVER FORGET!"

The White House said Sunday Trump has a duty to highlight Omar's comments and that the president wished no 'ill will' upon the first-term lawmaker. (Evan Vucci/Associated Press)

Critics accuse Omar of offering a flippant description of the assailants behind the attack that killed nearly 3,000 people. She later sought to defend herself by tweeting a quote from former U.S. President George W. Bush. Days after 9/11, the Republican president referred to the attackers as "people."

Bush had said, "The people — the people who knocked those buildings down will hear all of us soon."

"Was Bush downplaying the terrorist attack?" Omar asked.

Neither Trump's tweet nor the video included Omar's full quote nor the context of her comments, which were about Muslims feeling that their civil liberties had eroded after the attacks. The tweet continued to lead Trump's Twitter feed on Sunday, with more than nine million views.

White House press secretary Sarah Sanders questioned why Democrats weren't following Trump's example and calling out Omar, too. Democrats who criticized the president over the tweet defended Omar. Some also noted their past disagreements with her.

"Certainly the president is wishing no ill will and certainly not violence towards anyone, but the president is absolutely and should be calling out the congresswoman for her not only one time but history of anti-Semitic comments," Sanders said. "The bigger question is why aren't Democrats doing the same thing? It's absolutely abhorrent the comments that she continues to make and has made and they look the other way."

Speaker of the House Nancy Pelosi, shown April 10, said she is taking steps to ensure Omar's safety after death threats. (J. Scott Applewhite/Associated Press)

Omar's full quote, which Democrats argue was taken out of context:

"Here's the truth. For far too long we have lived with the discomfort of being a second-class citizen and, frankly, I'm tired of it, and every single Muslim in this country should be tired of it. Cair (Council on American-Islamic Relations) was founded after 9/11 because they recognized that some people did something and that all of us were starting to lose access to our civil liberties."

Omar later corrected her statement, saying Cair was formed earlier but doubled in size after 9/11.

.<a href="https://twitter.com/POTUS?ref_src=twsrc%5Etfw">@POTUS</a>, take down that hateful video that's inciting violence against <a href="https://twitter.com/Ilhan?ref_src=twsrc%5Etfw">@Ilhan</a> and her children! <a href="https://twitter.com/hashtag/TakeItDown?src=hash&ref_src=twsrc%5Etfw">#TakeItDown</a> —@RepSpeier

Omar repeatedly has pushed fellow Democrats into uncomfortable territory with criticism of Israel and the strength of the Jewish state's influence in Washington. She apologized for suggesting that lawmakers support Israel for pay and said she isn't criticizing Jews. But she refused to take back a tweet in which she suggested American supporters of Israel "pledge allegiance" to a foreign country.

Rep. Jerry Nadler, a New York Democrat whose constituents include Manhattan's financial district, which was targeted on Sept. 11, 2001, said he had no issues with Omar's characterization of the attack.

"I have had some problems with some of her other remarks, but not — but not with that one," he said.