Tehran accused on Monday Israel of being behind that air strike in Syria that left four Iranian "military advisers" dead. Iran “strongly” condemned the “flagrant” aggression against the Syrian regime’s T-4 airbase in Homs, Irans 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. Irans Fars news agency said "four Iranian military advisers" were killed in Mondays attack on the military airport. The news agency, which is close to the countrys Revolutionary Guards, had earlier reported that three Iranians had been killed. Some Iranian media reported that one of those killed was a member of the Revolutionary Guards Aerospace Force, a division that operates drones. More than 1,000 Iranians have been killed in Syria, including senior members of the Guards. The ministrys press release made no mention of the alleged victims. The Syrian Observatory for Human Rights, which monitors the countrys conflict, said 14 fighters were killed, including Syrian army officers and Iranian forces. The Syrian regime and Moscow also blamed Israel for carrying out Mondays strike. Russian Foreign Minister Sergei Lavrov said the strike on the T-4 base was a dangerous development. The Israeli army has refused to comment. Israel has carried out numerous raids inside Syria since 2013, targeting the regime and the Iranian-backed Lebanese “Hezbollah” group. Tensions between the Israel and Iran rose in February after an Israeli raid against a Syrian regime base. Israel had accused Iran of having launched a drone from the base towards Israeli airspace. Iran denounced the claims as "ridiculous". Israeli Intelligence Minister Yisrael Katz said at the time that his country would not accept "any Iranian military presence in Syria."