US denies role in scientist's death
The US played no role in the killing of an Iranian nuclear scientist, Secretary of State Hillary Clinton has said.
She added that America is looking for an international understanding with Iran to end its uranium enrichment programme.
Mrs Clinton categorically denied any US involvement in the death of Mostafa Ahmadi Roshan.
Reports said two assailants on a motorcycle attached a magnetic bomb to the professor's car, killing him and his driver.
Prof Roshan was a chemistry expert and director of the Natanz uranium enrichment facility in central Iran.
Mrs Clinton called recent Iranian threats to close off the Gulf "provocative and dangerous".
She said the US was committed to keeping the international waterway open, calling it "part of the lifeline that keeps oil and gas moving around the world".