(This story fixes dateline to July 13 and typo in eighth paragraph.))

FILE PHOTO: English Defence League leader Tommy Robinson arrives at Westminster Magistrates' Court in London September 11, 2013. REUTERS/Andrew Winning

LONDON (Reuters) - Sam Brownback, the U.S. Ambassador for International Religious Freedom, complained to the British ambassador in Washington D.C. about the treatment of an English right-wing activist who is in jail for disrupting a trial, according to three sources familiar with the discussion.

Brownback raised the case of the activist known as Tommy Robinson in a June meeting with Sir Kim Darroch, Britain’s Ambassador to the United States, according to a British official and two sources close to the organizers of a pro-Robinson demonstration planned for London on Saturday.

Robinson, whose real name is Stephen Yaxley-Lennon, though he also uses other aliases, is a founder of the English Defense League, which has organized violent demonstrations against Islamic immigrants in the UK in the past decade. More recently, Robinson has branded himself a journalist and campaigner against Islamic extremism, a move that won him contacts with American anti-Muslim activists.

Robinson was arrested in late May outside a courthouse in Leeds, England, while making video recordings about a trial related to child molestation and jailed for 13 months for violating English law limiting publicity during criminal trials.

Brownback raised the jailing of Robinson during a meeting with Darroch that covered a range of “religious freedom issues”, the British official confirmed earlier this week.

Brownback told Darroch that if Britain did not treat Robinson more sympathetically, the Trump administration might be compelled to criticize Britain’s handling of the case, according to the two sources in contact with organizers of the planned pro-Robinson demonstration.

The sources said Robinson’s supporters, who have also been in touch with the Trump administration about the issue, were concerned that he could be attacked by other prisoners.

Reuters was unable to determine why the top U.S. official responsible for defending religious freedom would try to intervene with the British government on behalf of an activist who has expressed anti-Islamic views.

Brownback, who is a former governor of Kansas and former U.S. senator, was not available for comment. However, on Thursday a U.S. State Department spokesman said the “characterizations” of Brownback’s meeting with Darroch by Reuters sources were “completely false” but the spokesman did not elaborate further.

The British Embassy had no comment on further details of the discussion.

Last week, the Middle East Forum, a Philadelphia group, said it was sponsoring and organizing a “Free Tommy Robinson” demonstration in London near the British Parliament on Saturday in collaboration with British and European groups.

The event was expected to merge with a demonstration in support of U.S. President Donald Trump, who appointed Brownback, according to the British newspaper The Independent.

Demonstration organizers said in a leaflet which circulated in London this week that Republican U.S. Congressman Paul Gosar and Dutch far-right leader Geert Wilders were scheduled to speak at its rally. U.S. Congressman Gosar did not immediately respond to a request for comment.

But Wilders tweeted on Thursday that he would not attend the rally because the U.K. Ambassador to the Netherlands, Peter Williams, told Dutch authorities Britain would not provide security for him.

British police said they were imposing restrictions on the event to “prevent serious disruptions” after protesters at a previous event made Nazi salutes and threw bottles at officers.

A spokesman for Hope Not Hate, a British anti-racism group, said, “In the week President Trump comes to the UK, his hand-picked diplomat allying himself with a far-right convicted fraudster perhaps shouldn’t be too much of a shock.”