(Reuters) - U.S. serviceman Gordon Black, detained in the Russian city of Vladivostok, has pleaded not guilty to charges of threatening to kill his girlfriend and partially guilty to theft charges, RIA news agency reported on Monday.

The state Russian agency, reporting from Black's second court hearing in Vladivostok, in Russia's Far East, said the U.S. soldier, who was stationed in South Korea but detained in Russia on May 2, spoke in court through an interpreter.

"No (I don't plead guilty to threatening to kill)," RIA cited Black as saying. "Partially (to the theft), there was no intent."

Black was detained on suspicion of stealing from his Russian girlfriend. Citing local prosecutors, Russian independent media reported he had also subsequently been charged with threatening to kill her.

RIA reported that Black pleaded guilty to theft charges in May but would enter a plea later and that he was co-operating with the investigators.

(Reporting by Lidia Kelly in Melbourne. Editing by Gerry Doyle)