WASHINGTON, Aug 7 (Reuters) - The arrest of Imran Khan is Pakistan's "internal matter", a US State Department spokesman said on Monday (Aug 7), declining to take a position on the legal troubles of the former prime minister and frequent US critic.

Police arrested Khan in Lahore on Saturday after a court sentenced him to three years in prison for illegally selling state gifts. The guilty verdict could stop the opposition leader from the Pakistan Tehreek-e-Insaf party from contesting a national election later this year.

Khan denies wrongdoing and maintains the government and the powerful military - which has run the country for about half of its 75-year history - imposed fabricated charges on him.

"We believe that is an internal matter for Pakistan," State Department spokesperson Matthew Miller said in a press briefing on Monday, when asked whether the US thought Khan got a fair trial.

"At times there are cases (around the world) that are so obviously unfounded that the United States believes it should say something about the matter. We have not made that determination here," Miller added.

Khan initially alleged that his ouster from office in a parliamentary vote last year was backed by Washington and orchestrated by Pakistan's top generals. Washington and the military both denied this.

Analysts noted that the US response to Khan's legal woes has been muted compared with the prosecution of other opposition figures around the world.

"I think Khan blaming the US for his ouster last year certainly hasn't helped matters for him. The US has since steered clear of commenting in any specific terms on Pakistan's politics," said Madiha Afzal, a fellow in the Foreign Policy program at Brookings Institution, a Washington-based think-tank.