Estonia’s ruling center-right Reform Party and the main opposition Center Party are in a close race in opinion polls ahead of a general election on Sunday that has seen campaigns dominated by socio-economic issues and an increased focus on national security in response to Russia’s moves in Ukraine.

A poll published by independent research company Turu-uuringute AS this week, showed that the pro-Russian Center Party is holding a 5 percentage point lead over Prime Minister Taavi Roivas’ Reform Party. Another poll published by...