When the US officials sought to investigate workers at the luxury St Petersburg where the poisoning allegedly happened they found there were no records of who had been on shift.
According to the official a formal note of protest was lodged with Russia by the US Sate Department.
US State Department spokesperson Elizabeth Kennedy Trudeau, said: "We are troubled, and we remain troubled, by the way our diplomatic and consular staff have been treated over the past two years.
"In particular, the harassment and surveillance of our diplomatic personnel in Moscow by security personnel and traffic police has increased significantly."
Earlier this year video footage emerged of a US diplomat and a Russian police officer in a scuffle outside the US Embassy in Moscow.
Both sides subsequently expelled two diplomats each in a Cold War-style standoff.
It is not unknown for foreign tourists and businessmen to be drugged in Russia, but the location in an upmarket hotel was unusual and there was no attempt to rob either of the US officials.