By Daniel Wallis

(Reuters) - A Washington-based journalist has sued St. Louis County and one of its police lieutenants, saying his rights were violated when he was arrested while covering protests over the killing of an unarmed black teenager by a white police officer in Ferguson, court papers showed.

Gerald Yingst, a reporter and producer with News2Share, also accuses police of defaming him by announcing his arrest on Twitter and saying he had refused a commander's order to clear the street, damaging his professional reputation.

A St. Louis Police Department spokesman referred enquires about the lawsuit to the St. Louis County counselor's office. No one answered calls placed there on Thursday evening.

Yingst was one of two people detained on Nov. 22 during one of the nightly protests outside the Ferguson police department as a grand jury mulled whether to charge Darren Wilson with the shooting death in August of 18-year-old Michael Brown.

The grand jury eventually declined to indict the officer, prompting two days of violent demonstrations in the St. Louis suburb, as well as wider protests and national soul-searching over policing.

Yingst's lawsuit, filed on Tuesday in U.S. District Court in Missouri, names St. Louis Police Lieutenant James Vollmer as a defendant and says he is being sued in his individual capacity. It also sues St. Louis County for allegedly failing to train and supervise Vollmer, and for defamation.

The lawsuit says Yingst was standing on the sidewalk outside the police headquarters, recording attempts by officers to clear protesters from the street, when Vollmer allegedly pointed at Yingst and told a group of patrolmen to "lock him up."

Protesters and other reporters standing alongside Yingst on the sidewalk were not arrested, it said. "No reasonable officer would have believed that Defendant Vollmer had probable cause to cause Yingst's arrest," the lawsuit added.

Shortly afterward, the police department tweeted, using the journalist's official Twitter handle: "@TreyYingst reporter from D.C. taken into custody for failure to disperse. Was asked to leave street by the commander and refused. #Ferguson."

The lawsuit, which was filed for Yingst by attorneys from the American Civil Liberties Union, accuses the county of publicly disclosing information that it knew to be false, and of harming the reporter's professional reputation in the process.

(Reporting by Daniel Wallis in Denver; Editing by Mohammad Zargham)