Republican presidential candidate Donald Trump takes questions from reporters Saturday in West Palm Beach, Fla. (Jabin Botsford/The Washington Post)

A group opposed to Donald Trump is set to announce Monday that it will pour an additional $1 million into television advertisements in Florida, where the March 15 primary is considered the key battleground in the bid to stop the Republican presidential front-runner's momentum.

American Future Fund, which already is waging a $1.75 million ad campaign across Florida to discredit Trump, is adding $1 million to its ad buy there for the final week before the primary.

"We’re seeing a tightening race in Florida, a real opportunity to stop him," said Stuart Roy, a spokesman for American Future Fund, a tax-exempt "social welfare" organization based in Iowa.

The move will expand the rotation of three types of ads already airing in Florida. One series features testimonials from people who claim they were duped by Trump University, the for-profit real estate training program bearing Trump's name that is the subject of civil fraud litigation.

Other ads include one highlighting shady business associates of Trump and one featuring veterans speaking out against him over his dismissal of Sen. John McCain's service in Vietnam. The latter is airing in the Florida Panhandle region, where many military members and veterans live.

The Florida ads are the latest in a broader effort to arrest Trump's momentum in Florida and in other states holding winner-take-all primaries on March 15.

An affiliated group, American Future Fund Political Action, on Monday announced a six-figure ad buy in Florida with an ad highlighting Trump's outbursts of profanity and vulgarity.

The ad shows Trump vowing, "I'm very highly educated... I have the best words," then cuts to scenes of him at public appearances uttering profanities that are bleeped out. It will air starting Tuesday in the Pensacola and Panama City markets, both conservatives areas of Florida.

"Donald Trump’s repeated public reliance on profanities and vulgarities to express himself is one more piece in an ever-mounting pile of evidence that he does not have the temperament or moral integrity to lead the world’s greatest nation," said Roy, also a spokesman for the American Future Fund Political Action.