The planned visit to Russia of the father of US intelligence leaker Edward Snowden is to be kept strictly secret, with details of their meeting to be made public only after it has happened, a report said Wednesday.

Snowden received asylum in Russia on August 1, enabling him to leave the Moscow airport where he had been holed up for more than five weeks after arriving from Hong Kong.

His current whereabouts in Russia are unknown.

His father Lon Snowden has said in US media interviews that he has obtained a Russian visa but has not revealed when he will make the trip.

"The visit of Snowden senior and those accompanying him will, for obvious reasons, have a confidential character," the Interfax news agency quoted a source familiar with the situation as saying.

"The world will find out about it post-factum, after the father has met the son at a secret location," the source added.

Snowden's Russian lawyer Anatoly Kucherena -- who has been the sole source of information on the 30-year-old American in Russia -- has gone on holiday for the rest of August, according to his office.

The United States wants to put Snowden on trial under the Espionage Act for leaking details of a vast US telephone and Internet surveillance programme, but Russia has refused to extradite him.