A longtime security official and his wife have been detained in Estonia on suspicion of passing classified information and state secrets to Russia, prosecutors said Wednesday in a case likely to add to long-standing tensions between the two countries.

Aleksei Dressen, who works for Estonia's security police, and his wife, Viktoria Dressen, were arrested at Tallinn Airport as she was boarding a flight to Moscow, prosecutors said. Aleksei Dressen went to the airport to give his wife a folder that contained classified information, said Kadri Tammai, a spokeswoman for the prosecution.

Viktoria Dressen, who does not work for the government, was allegedly acting as a courier, forwarding information to Russia's main security agency, the FSB, that her husband had collected "over a period of several years," Tammai said.

Aleksei Dressen had access to documents considered state secrets, she said, though she declined to elaborate. "Based on what we know at this point, we can say that this is quite a serious case for Estonia," Tammai said.

Estonia is extremely distrustful of its enormous eastern neighbor. Security officials and politicians claim that Russia's intelligence community has increased activities in the Baltic region _ including Estonia, Latvia and Lithuania _ since the three countries joined NATO and the European Union in 2004.

Aleksei Dressen, born in 1968, has worked for Estonia's security police for nearly 20 years and most recently dealt with domestic security and extremist groups in the Baltic state. Prior to Estonia's renewal of independence from the Soviet Union in 1991, he had worked in the police force.

If found guilty of treason, Dressen faces a prison sentence of 20 years to life, Tammai said.

The chief of Estonia's security police, Raivo Aeg, said the incident showed that countries hostile to the Baltic nation have a keen interest to learn about its security matters and that Dressen's case serves as "a warning to us all".

The arrests sparked memories of another recent Estonian spy case. In 2009, one of Estonia's top security officials, Hermann Simm, was sentenced to 12 1/2 years in prison after being convicted of treason for passing domestic and NATO secrets to Russia in a case that shocked the tiny nation of 1.3 million.

The case turned out to be one of the most damaging in the history of NATO.