A fire broke out at the headquarters of the highly-secretive Russian Foreign Intelligence service (SVR) on the outskirts of Moscow on Wednesday, the agency told AFP.
"There is a fire on the site," a spokeswoman for the service who declined to give her name told AFP.
"We cannot provide any further comment until the situation becomes clearer."
Three people became trapped in the basement of the building just south of the capital, Interfax news agency quoted a source as saying, but the head of SVR's press service Sergei Ivanov later said that "nobody was hurt".
"The fire has been localised," he told Russian agencies.
More than 15 fire trucks were sent to tackle the blaze, which started at the site of repair works in the basement, Interfax reported.