Image copyright Getty Images Image caption Mr Clarke allegedly ordered his men to detain and question a fellow passenger after a flight

A Wisconsin sheriff known for his outspoken support of Donald Trump is accused of ordering staff to unlawfully detain a man over a brief exchange.

Sheriff David Clarke is being sued by Dan Black, who claims he was held after he spoke to the police official on board a flight from Texas to Wisconsin.

Mr Clarke allegedly texted a police official to follow Mr Black to baggage at the airport, federal records show.

He claims Mr Black stood over him in a "physically threatening manner".

"Just a field interview, no arrest unless he becomes an a**hole with your guys," the Milwaukee County sheriff allegedly wrote in a text message to Captain Mark Witek, the Milwaukee Journal-Setinel reported.

"Question for him is why he said anything to me. Why didn't he just keep his mouth shut. Follow him to baggage and out the door. You can escort me to carousel after I point him out."

A copy of the text messages was given to the newspaper by an attorney for Mr Black, who is suing the sheriff, Milwaukee County and several deputies over the matter.

A spokeswoman for the sheriff, Fran McLaughlin, declined to comment on the text messages, according to the newspaper.

Mr Black said he approached Mr Clarke to ask him if he was the sheriff after boarding a flight from Fort-Worth Dallas, Texas, to Milwaukee, Wisconsin, on 15 January.

He claimed he shook his head after the sheriff asked him if he had a problem and walked away.

Mr Black said he was later detained, questioned and escorted out of the airport upon arrival by several officers in uniform and a police dog.

Who is David Clarke?

The 60-year-old African-American Democrat has been Milwaukee County sheriff since 2002

Spoke in support of President Trump at the Republican National Convention in July

Gun rights advocate who is a vocal critic of the Black Lives Matter movement

Presides over a jail under scrutiny for the deaths of four inmates in 2016. Several jail employees face criminal charges in connection to one of the deaths

Announced he had been appointed as an assistant secretary for the Department of Homeland Security, but the White House has not confirmed the appointment

Accused of plagiarising parts of his 2013 master's thesis, according to a CNN report. He has denied the claim

The sheriff's lawyers claim Mr Black approached Mr Clarke, stood over him in a threatening manner and stared before he "shook his head at him for a prolonged period of time", according to court records.

Federal investigators launched an inquiry into the incident, but said earlier this month they would not criminally prosecute any civil rights offences.

Image copyright Getty Images Image caption Mr Clarke drew national attention as a Democrat in support of Donald Trump

After Mr Black filed the complaint in January, the sheriff's office mocked him in a Facebook post, calling him a "snowflake" and saying anyone who would harass him on a plane might get "knocked out".

Milwaukee County auditors are also probing whether Mr Clarke abused resources in ordering Mr Black's detention.