CHISINAU (Reuters) -A Moldovan security official accused Russia on Sunday of "massive interference" as Moldovans voted in a tightly fought presidential election that could see Moscow claw back influence in a country drawing closer to the European Union.

A former Soviet republic flanked by Ukraine and Romania and one of Europe's poorest countries, Moldova has a population of 2.5 million. It also has a large expat population of 1.2 million, whose votes could prove key to Maia Sandu in the run-off.

Moldovans vote on Sunday in a presidential runoff that has been overshadowed by election meddling allegations and could see Moscow gain more influence in a diplomatic battleground between Russia and the European Union.

Moldovans cast votes in a decisive presidential runoff Sunday that pits pro-Western incumbent Maia Sandu against a Russia-friendly opponent, as ongoing claims of voter fraud and intimidation threaten democracy in the European Union candidate country.

The man challenging Moldova's pro-EU leader Maia Sandu for the presidency has taken a narrow lead, according to preliminary results, in a pivotal presidential election run-off seen as a choice between Europe and Russia.

Moldova has told several EU nations that it believes Russia will try to disrupt voting by Moldovan expatriates at polling stations abroad in Sunday's presidential election, a Moldovan government source said.