U.S. House Speaker Paul Ryan's political operation sent a cease-and-desist letter on Thursday to a group that is trying to draft him as a Republican presidential candidate, urging it to halt its activities and warning of legal risk.

With establishment Republicans desperately searching for a way to stop real estate businessman and former reality TV personality Donald Trump's march toward the party's nomination for the Nov. 8 presidential election, Ryan's name has been mentioned often as an alternative. But he has said he does not want to run for president this year and has disavowed the Committee to Draft Speaker Ryan group.

The organization has continued attempts to collect one million signatures on an online petition to draft Ryan, arguing that the very definition of a draft movement is to encourage a reluctant participant to join.

The Draft Ryan group was another indication of Ryan's rise to the Republican Party's top ranks since he became speaker of the House of Representatives last year. Ryan, a Wisconsin congressman, was Mitt Romney's vice-presidential running mate on the Republicans' 2012 ticket.

A spokesman for Draft Ryan, David Catalfamo, said the letter was "a sad commentary on the state of our politics today," adding, "The Committee to Draft Speaker Ryan is simply a patriotic effort to save our party and save our country." The group registered with the U.S. Federal Election Commission as a Super PAC, an independent political action committee that may raise unlimited sums of money.

Timothy Kronquist, an attorney for Ryan's political operation, addressed the letter to the group's treasurer, David Satterfield. It urged the group to immediately cease and desist from any representations that it is acting on Ryan's behalf or raising funds that would assist Ryan's campaign activities.

"We believe the actions of your organization are not in compliance with federal law and may constitute fraudulent solicitation of funds," the letter said.

"Speaker Ryan has repeatedly announced publicly that he is not running for president in 2016. ... It is in the public interest for your organization to cease potentially confusing and misleading people into supporting your organization."

Ryan succeeded John Boehner in his current role late last year, but he debated taking on the position due to the demands on his young family.

A copy of the letter, which was dated Thursday, was seen by Reuters.

Fundraising denials

A person close to Draft Ryan said the group had removed the "donate" button from its website to clarify that the effort is not a fundraising exercise, and said the site would be changed so people can sign the petition without leaving their email addresses.

He said the effort so far had been funded by Earle Mack, a former U.S. ambassador to Finland. Mack has told The New York Times that he would spend up to $1 million US on the Draft Ryan committee.

Mack showed no sign of backing down on Thursday afternoon in an interview with Fox Business News, saying Draft Ryan only sought to propose Ryan as a unifying candidate in the event Republicans deadlock over who should be their nominee at the party convention in July.

"Let me tell your viewers to please go to Draft Speaker Ryan.com. We're collecting a million signatures to raise the awareness that we love the speaker, and the speaker is the right man for the job," Mack said.

Asked whether Ryan might not want the nomination, Mack acknowledged, "I don't even know the man."

Trump has racked up primary wins and expanded his lead this week despite attacks from the party's establishment, which is trying to stop him from claiming the nomination at the Republican convention in July.

Ryan has abstained from endorsing any presidential candidate in the 2016 race.