The top Democrat in the US Congress has ordered a safety review for a Muslim congresswoman and her family after accusing President Donald Trump of putting her in danger by tweeting a video of her spliced with footage of the 9/11 attacks.

House Speaker Nancy Pelosi took time out from an official trip to issue a strong statement urging Mr Trump to remove the clip featuring Minnesota congresswoman Ilhan Omar.

"Following the president's tweet, I spoke with the sergeant-at-arms to ensure that Capitol Police are conducting a security assessment to safeguard Congresswoman Omar, her family and her staff," she said.

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

Mr Trump's spokeswoman Sarah Sanders has defended the president against accusations that he was inciting violence toward the Muslim congresswoman.

Ms Omar has been at the centre of an escalating row after a clip emerged of her characterising the deadliest attack on US soil as "some people did something."

On Friday, President Trump tweeted a video that juxtaposed the snippet, which Ms Omar's fellow Democrats say was taken out of context, with images of the hijacked planes used in the attacks crashing into the Twin Towers that once dominated New York's skyline.

Menacing music accompanies Ms Omar's words.

The clip, which had been viewed more than 9.4 million times, ends with the words: "SEPTEMBER 11 2001 WE REMEMBER."

Democrats including Beto O'Rourke, Kamala Harris and Ms Omar's fellow first-time Congresswoman Alexandria Ocasio-Cortez were quick to rush to Ms Omar's defence, accusing the president and other Republicans of deliberately de-contextualising her remarks and endangering her life.

Ms Sanders, however, defended Mr Trump, telling ABC's This Week that "the president is wishing no ill will and certainly not violence towards anyone."

She added: "It's absolutely abhorrent the comments she continues to make and has made and (Democrats) look the other way.

"I find her comments to be absolutely disgraceful and unbefitting of a member of Congress and I think that it's a good thing that the president is calling her out for those comments, and the big question is why aren't Democrats doing it as well."

Ilhan Omar is the first African-born American, and one of the first two Muslim American women to serve in the US Congress.

She mounted her own trenchant fight back, tweeting: "No one person - no matter how corrupt, inept, or vicious - can threaten my unwavering love for America.

"I stand undeterred to continue fighting for equal opportunity in our pursuit of happiness for all Americans," she said.

Ilhan Omar is the first Somali-American, first African-born American, and one of the first two Muslim American women to serve in the US Congress

The controversy arose after Ms Omar delivered a 20-minute address to the Council on American Islamic Relations (CAIR) shortly after the New Zealand mosque attacks in March.

"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," she said.

"CAIR was founded after 9/11," she added, "because they recognised that some people did something and that all of us were starting to lose access to our civil liberties."

The civil rights group was in fact founded in 1994 but grew significantly after 2001.

The speech did not initially receive significant attention until the snippet in question was highlighted weeks later by controversial Australian personality Mohammad Tawhidi who refers to himself as the "Imam of Peace."