Mikhail Khodorkovsky, the head of Russia's largest oil producer, Yukos, was detained early Saturday by security forces at an airport in Siberia, the Interfax news agency reported, citing Yukos company officials. For months, the Russian prosecutor's office has been investigating Yukos company officials and Yukos shareholders seeking evidence of tax evasion and theft of state property. Yukos spokesman was quoted by Interfax as saying that the plane was surrounded by trucks after it landed in Novosibirsk for a refuelling stop. The prosecutor's office confirmed that Khodorkovsky was detained because he had failed to appear for questioning on Friday as summoned, according to Interfax.