The Islamic Republic has expelled four Azerbaijani diplomats as tensions simmer between Tehran and Baku.

The Iranian state news agency IRNA reported the move on Friday, saying that four diplomats in Tehran and Tabriz have been declared as “persona non grata” and should leave the country immediately.

Describing the measure as a tit-for-tat action, the report said it was a response to Azerbaijan's expelling four Iranian diplomats in early April.

Azerbaijan had said it was expelling the Iranian diplomats over "provocative actions" referring to a series of actions in recent months including military exercises carried out by Iran's armed forces on the border. Baku's decision was announced shortly after it arrested six Iran-funded agents accused of a coup plot.

In January, a gun attack at the Azerbaijan embassy in Tehran left one man dead and last month, there was an attempted murder by what is believed to be an Iranian cell, of Azerbaijani MP, Fazil Mustafa.

The move was seen in part due to Baku's improving relations with Tehran's archnemesis Israel, the dispute spiking when Baku opened an embassy in Israel in late March, slammed by Iran as an anti-Iranian move, a claim denied by Azerbaijan.

Tehran accuses Baku of harboring Israeli intelligence and military elements that plan to use its territory in a possible attack against Iran’s nuclear installations.

Around a quarter of Iran’s population is Azari, with analysts and activists disagreeing over the closeness of their cultural and linguistic links to their neighbors to the north.