Russia and Greece were poised on Wednesday to expel two of each other’s diplomats in a rare dispute that Greek media said had been prompted by the issue of Macedonia, which expects this week to be formally invited to join the NATO alliance.

Greece had informed Russia on July 6 that it planned to expel Russian diplomats from the country for illegal activities connected to rallies against a deal with Macedonia, a Greek diplomatic source told Reuters on Wednesday.

That deal - whereby Macedonia will become formally known as the Northern Republic of Macedonia - will unlock a formal invitation from NATO for the tiny ex-Yugoslav republic to join the bloc, a move strongly opposed by Moscow.

Russia’s foreign ministry said it would respond in kind to the expulsions, Interfax news agency reported.

"We had issued warnings to Russian authorities for some time over (the actions of) these specific 4 diplomats and civilians, and on Friday it was officially raised, giving them a reasonable period of a few days to leave the country," the Greek source told Reuters.

The allegations also included attempts to offer money to state officials, the source said.