"Yes it is true we've had an agreement with Russia since 1993 on transit visa-free travel through Latvia, but European Union rules say citizens of a third country need visas as well as transit visas to enter and travel within the EU," said Alda Vanaga, acting head of the Foreign Ministry's councilor department.
"We will open a Latvian consular office in three months in Kaliningrad, and Russia will be officially notified about the new requirements."
Officials at the Russian Embassy in Latvia are awaiting the legislation before commenting on the decision.
"We will not act until we have been officially informed by the Latvian government on this issue," Leonid Budakov, spokesman for the Russian Embassy, said.
Russia is reportedly planning to re-route the St. Petersburg to Kalinin-grad train through Lithuania should the Latvian government insist on its decision. This, however, does not change much for Russian nationals.
Petras Zapolskas, spokesman for the Lithuanian Ministry of Foreign Affairs, said Lithuania has an agreement with Russia on transit visa-free travel, but it only works one way.
"Russian citizens from Russia traveling through Lithuania need a transit visa, but Russian citizens in Kaliningrad traveling through our country do not need one," Zapolskas said.
The Latvian Ministry of Transport would not comment on what it would mean for Latvia if the St. Petersburg-Kaliningrad train is rerouted through Lithuania.
In Moscow, diplomats have reacted strongly against the Latvian government's decision, saying the whole question is about Latvia's fear of Russian extremists entering Latvia illegally.
Late last year, four members of the pro-Soviet National Bolsheviks were detained in the eastern Latvian town of Daugavpils for crossing the border illegally, and another three were arrested and charged with terrorism after they stormed St. Peter's Church's tower in Riga's Old Town, threatening to throw grenades and blow themselves up along with the church tower.