Russian authorities say they have detained a serviceman and his brother for having allegedly passed state secrets to neighboring Estonia.
A criminal case has been opened for high treason, the Federal Security Service(FSB)said in a statement on October 6.
It did not provide details of any information that had been passed on to the Estonian special services.
"There hasn't been any official correspondence with Russia on that issue," Reuters quoted Estonia's Foreign Ministry as saying in a statement.
The serviceman was detained in the western Russian city of Smolensk, while his brother, a permanent resident of Estonia, was detained in Pskov, near the Estonian border.
The men could face up to 20 years in jail, if convicted.