By Sarah Rainsford
BBC News, Moscow
A Russian official has said that the whereabouts of two Russian agents convicted in Qatar of assassinating a former Chechen president are unclear.
The agents had been expected to serve their sentence in Russia
Yuri Kalinin, an official with Russia's prisons authority admitted the men were not being held in any of his jails.
The two men were given a life sentence in Doha last year, for planting the car bomb that killed Zelimkhan Yanderbiyev.
Russia had wanted him extradited, saying he was sending funds to rebels, but Moscow denied ordering the killing.
Mr Kalinin suggested the two intelligence agents may be undergoing medical treatment, but had no further information. And, in perhaps his most telling comment, he added that a sentence handed down in Qatar was irrelevant here in Russia.
The agents were returned to Moscow in December in what appeared to be a goodwill gesture by Doha. Their arrest and conviction for assassination had threatened to cause a major breach in relations.
The details of the deal that brought them home are a mystery, but it had been thought the men would be obliged to serve out their sentence.
Moscow, though, always insisted they were innocent, claiming its agents were in Doha to gather intelligence for the international war on terror.