A flame-haired female Russian student was a Kremlin spy who offered sex as she sought to make influential connections in the US political system, a court heard.

Maria Butina, 29, took part in a "years-long conspiracy" to secretly advance the interests of the Russian government in America, it was alleged.

Butina appeared in court in Washington on Wednesday and pleaded not guilty to charges of conspiracy, and acting as a foreign agent, which carry a possible 10-year jail term.

Dressed in an orange jump suit, and pink training shoes, she showed little emotion and said nothing, taking copious handwritten notes during a lengthy hearing.

Judge Deborah Robinson denied bail, saying there was no other way to prevent Butina seeking diplomatic refuge at the Russian Embassy.