Nato will defend Bulgaria against any Iranian retaliation for hosting US tanker aircraft, alliance spokesman Colonel Martin O'Donnell told Euronews on July 23, a day after the Bulgarian parliament approved the deployment.

The vote draws a European Union and Nato member state directly into the logistics chain of the US campaign against Iran at a point when several allies have refused. Italy and Spain have blocked US Air Force aircraft involved in the operation, leaving Washington short of basing options and prompting friction inside the alliance over burden-sharing.

Iranian officials and media have noted the use of Bulgarian and British airfields in the ongoing military buildup against Iran, which is expected in the next few days, according to analysts currently monitoring the situation between Tehran and Washington. 

The National Assembly authorised the stationing of up to eight KC-135 aerial refuelling aircraft and 250 US military personnel by 136 votes to 13, with two abstentions. The aircraft are to be based at Bezmer Air Base, about 260 km southeast of Sofia, from July 24 to October 1.

The deployment falls under a bilateral defence cooperation agreement signed in 2006, which designated Bezmer for joint use by Bulgarian and US forces.

Iranian foreign ministry spokesman Esmail Baghaei had warned Sofia on July 21 that facilitating US attacks would amount to complicity in "aggression and war crimes", according to Iranian state media, and urged Bulgaria not to become "an accomplice of aggressors and lawbreakers," Persian language media previously reported.

Bulgarian Prime Minister Rumen Radev said it was "categorically out of the question for military operations in the Middle East to be conducted from Bulgarian territory", adding that the aircraft were intended solely for logistical missions and would refuel outside Bulgarian airspace.

O'Donnell pointed to earlier Iranian missile fire towards Turkey. "We saw when Iran fired missiles towards Turkey, a Nato ally, that Nato defended in all of those instances, and we will continue to defend against any threat posed by Iran or anyone else to this defensive alliance," he said, Euronews.

Mayors of five municipalities around Bezmer raised security concerns over hosting the aircraft.

Iranian officials have already warned British officials of a potential retaliation against its airbases and assets in the Middle East and Cyprus, after previously being the targeted in the so-called 12-day war. 

British officials have also vacated the embassy on Ferdowsi Street in Tehran on July 22, according to an official notice seen by IntelliNews, following warnings from top Iranian diplomats that British assets would be potential targets for aligned groups.