Tehran accused Israel on Monday of "flagrant" aggression in Syria after an air strike hit a regime base killing four Iranian "military advisers", Iranian media said. The Islamic Republic condemned "strongly the aggression and the air strike by the Zionist regime" against the T-4 airbase in Homs, Iran's foreign ministry said in a statement.
The ministry called on "all free states... to not be indifferent to this flagrant Zionist aggression", adding that the air strike further complicated the situation in the war-torn country. Iran's Fars news agency said "four Iranian military advisers" were killed in Monday's attack on the military airport. The news agency, which is close to the country's elite Revolutionary Guards, had earlier reported that three Iranians had "fallen as martyrs". The ministry's press release made no mention of the alleged victims.
The Syrian Observatory for Human Rights, which monitors the country's conflict, said 14 fighters were killed, including Syrian army officers and Iranian forces.
Tehran, along with Moscow, is one Syrian President Bashar al-Assad's main allies and has played an important role in his recent victories. The Syrian regime and Moscow also blamed Israel for carrying out Monday's strike.
The Israeli army has refused to comment.
Israel is believed to have carried out numerous raids inside Syria since 2013, targeting the regime and its Lebanese arch-foe Hezbollah, which is backed by Iran.
Iran has deployed thousands of fighters to Syria, presented as "volunteers" from Afghanistan and Pakistan and trained locally by Iranian "military advisers."
Clement Therme, a researcher at London's International Institute for Strategic Studies (IISS), estimated the number of Afghan fighters in Syria at "between 10 and 20 thousand."
Iranian forces sent to Syria are there in a more "advisory than fighting" capacity given their low death toll in comparison to that of the Lebanese Hezbollah militia or Afghans, added the Iran expert.
Iran does not recognise the existence of Israel, which views Tehran as an existential threat and regularly denounces Tehran's support for Hezbollah, a powerful presence on Israel's northern border. Israel regularly worries about the Iranian presence in Syria, fearing the long-term establishment of hostile forces in the neighbouring country. Tensions between the two foes rose in February after an Israeli raid against a Syrian military base. Israel had accused Iran of having launched a drone from the base towards Israeli airspace. Iran denounced the claims as "ridiculous".