A senior Estonian state security official was arrested on suspicion of treason Wednesday as he prepared to board a Moscow-bound flight, a state prosecutor said.

Prosecutors allege Aleksei Dressen, 44, an officer in Estonia's Security Police, illegally collected classified information for years in Estonia after the Baltic republic broke free from the crumbling Soviet Union in 1991.

Relations between Moscow and Tallinn have been fraught with tension ever since, especially since Estonia, a Baltic nation of 1.3 million, joined the European Union and the NATO Western defence alliance in 2004.

"Dressen is suspected of collecting classified information for years and was caught with evidence," state prosecutor Norman Aas told reporters in the capital Tallinn.

"His wife was also arrested Wednesday morning at Tallinn airport as the couple planned to board a Tallinn-Moscow flight," Aas said.

The woman, identified as Viktoria Dressen, is suspected of being a courier for the illegally obtained classified information, he added.

In what prosecutors said was an unrelated case, Herman Simm, a former senior Estonian defence ministry official convicted of treason in 2009, was sentenced to 12 and a half years in prison for selling Russia NATO secrets for years.

Under Estonian law, treason carries a prison sentence of three to 15 years.

According to Estonian government records quoted by media, both Dressen and Simm were appointed in 1999 to the state strategic goods import and export control commission then headed by former Estonian foreign minister and current President Toomas-Hendrik Ilves.

Dressen worked on the commission for two years.