TALLINN (Reuters) - Three men have been jailed for spying for Russia, Estonia’s state prosecutor’s office said on Tuesday, an unusual case targeting low-level smugglers that comes amid heightened concern over muscular Russian foreign policy in eastern Europe.

Relations between Estonia, a north-eastern Baltic country and a member of the EU and NATO since 2004, and Russia, its eastern neighbor and former ruler, are increasingly tense after Russian special forces occupied Ukraine’s Crimea region a year ago.

The three men, whose ages range from 21 to 42, received sentences ranging from two years to four years and ten months for supplying information to Russian security services on the movements and operations of Estonia’s security service, defense forces and border guards.

The men, described as smugglers by the prosecutor’s office, were sentenced in closed trials for collaborating with Russian security services between October 2015 and February 2016.

There have been several high profile trials in Estonia of officials accused of spying for Russia in the last decade, but the prosecution of low-level informants with no access to state secrets indicates a heightened level of vigilance.

“The information on the trials and sentencing was released now as two of the trails were held behind closed doors, due to the nature of the crimes committed,” Ilmar Kahro, spokesman for the state prosecutor’s office told Reuters.

The Estonian Internal Security Service spokesman told a news conference in the southern Estonian town of Tartu that the men were not public servants and had no access to Estonia’s or any other country’s state secrets.