President Donald Trump speaks at Nuss Truck and Equipment in Burnsville, Minnesota. Photo: AP Photo/Susan Walsh.

Washington - US President Donald Trump continued to attack a Muslim congresswoman on Monday, even after she reported receiving an increase in death threats following previous messages targeting her.

Trump on Friday tweeted a video of Representative Ilhan Omar giving a speech about the treatment of Muslims after the September, 11, 2001 attacks, spliced with images of the World Trade Centre on fire. "WE WILL NEVER FORGET!" he wrote.

Omar said on Sunday the video sparked threats against her. Leading members of Omar's centre-left Democrat party have stepped up to defend her, including several presidential candidates.

House Speaker Nancy Pelosi said she had asked officials to review security measures in place to protect Omar.

Trump's latest salvo on Monday attacked both Omar and Pelosi.

"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!" Trump said on Twitter.

Trump, who has refused to take down the video using the September 11 imagery, is fundraising in Omar's home state Minnesota on Monday, and tweeted about his trip.

Omar quickly tweeted back at Trump, saying: "The Great State of Minnesota, where we don't only welcome immigrants, we send them to Washington." 

Omar, who fled the civil war in Somalia with her family when she was eight and later was able to claim refuge in the US, became last year one of the first two Muslim women to be elected to Congress.

The freshman Democrat has been critical of Israeli policies towards Palestinians and also raised questions about the influence of pro-Israel lobbying in Washington, triggering some accusations of anti-Semitism, which she denied.