Iran has expelled four Azerbaijani diplomats, state media reported Friday, saying the move was "in response" to Baku's expulsion of Iranian embassy staff in April after months of tensions.

"Four diplomats from the Ministry of Foreign Affairs of the Republic of Azerbaijan, declared personae non gratae, were expelled from Iran last month," official news agency IRNA said.

It said the Iranian foreign ministry's "action... was carried out in response to Baku's expulsion of Iranian diplomats."

Azerbaijan's foreign ministry early last month said it had notified the Iranian ambassador that "four employees of the Iranian embassy were declared personae non gratae" with 48 hours to leave the country.

Baku accused the embassy staff of carrying out activities "incompatible with diplomatic status" but did not elaborate.

Ties between neighbours Azerbaijan and Iran soured in January as a gunman stormed into Baku's embassy in Tehran, killed a diplomat and wounded two embassy security guards.

The Azerbaijani foreign ministry blamed Iran for the shooting, with spokesman Ayxan Hacizada saying an anti-Azerbaijani campaign had "encouraged the attack".

Iran's foreign ministry spokesman Nasser Kanani said Tehran strongly condemned the attack, claiming the motivations behind it were "personal".

Relations between the two countries have traditionally been strained, with the former Soviet republic a close ally of Iran's historical rival Turkey.

Tehran also fears that Azerbaijani territory could be used for a possible offensive against Iran by Israel, a major arms supplier to Baku.