The murder of British MP Jo Cox last summer shone a spotlight on the group, as her killer reportedly shouted “Britain first” as he ran towards her.
While there is no proof that he was referencing the group specifically –- and the party’s leader, Paul Golding, dismissed the reports as hearsay and called the attack a “heinous crime.”
Jo's widower, Brendan Cox, today tweeted that Trump should be "ashamed of himself" for "spreading hatred."
Fransen is the group's 31-year-old deputy leader. Fransen currently faces a charge of religious or racially aggravated harassment, according to police in Kent, England. She has been released on bail before a trial set to start on Jan. 29, police said. She pleaded not guilty.
On Twitter Wednesday, she thanked Trump for retweeting her and wrote, "I'm facing prison for criticising Islam. Britain is now Sharia compliant. I need your help! God bless."
Trump today retweeted three unverified, anti-Muslim videos posted by Fransen. One of the three tweets includes video with the caption "Islamist mob pushes teenage boy off roof and beats him to death!" while another reads, "Muslim Destroys a Statue of Virgin Mary!" Another video claims to show a "Muslim migrant" beating up a "Dutch boy on crutches."
The authenticity of the videos Trump retweeted from Fransen's timeline has not been independently verified, but all allege various crimes or violence by Muslims. At least one has been debunked: the individual referred to as a "Muslim migrant" assaulting a man on crutches in Holland was discovered to be neither Muslim nor a migrant, police and prosecutors told ABC News.
Anti-Muslim and anti-immigrant backlash is an issue in the U.K., however. British government statistics show a marked increase in hate crimes against minorities in the weeks following the Brexit vote. Some fear the decision to leave the EU has empowered the far right in the United Kingdom.
Trump has already come under fire for retweeting Fransen, including from the British government itself.
"Britain First seeks to divide communities through their use of hateful narratives which peddle lies and stoke tensions. They cause anxiety to law-abiding people," the prime minister's office said in a statement Wednesday. "British people overwhelmingly reject the prejudiced rhetoric of the far-right, which is the antithesis of the values that this country represents – decency, tolerance and respect."
"It is wrong for the president to have done this," the statement added.
But White House press secretary Sarah Sanders insisted the president was not pushing an anti-Muslim propaganda or offering an endorsement of the group when he retweeted Fransen, but instead making the case for national security.
"It’s important to talk about national security and national security threats,” Sanders said. “The president sees different things to be a national security threat and he sees having strong borders as being one of the things that helps protect people in this country from some real threats we face."
“Whether it’s a real video, the threat is real and that is what the president is talking about, that’s what the president is focused on, is dealing with those real threats and those are real no matter how you’re looking at it,” she said.
ABC News' Alexandra Faul and Lena Masri contributed to this report.