Reuters news agency quotes a Foreign Ministry spokesman as saying Serbian authorities do not know where Mladic is.
Earlier, the Dutch news agency ANP quoted Bot as saying Serbian authorities are negotiating with Mladic over his surrender.
The spokesman said Bot had only heard that Mladic was sick and may be in touch with his own people to surrender.
The past few days have seen a flurry of unconfirmed media reports that Mladic has been captured or that negotiations are under way for his surrender.
Those reports have been denied by the Serbian government and the UN war crimes tribunal in The Hague.
(with material from Reuters, AFP)