Iran's security council Saturday warned the United States against further attacks on its proxy bases in Syria stressing that any further strikes will be countered immediately.

Supreme National Security Council spokesman Keyvan Khosravi issued the warning following reports about an increase in casualties of US attacks on pro-Iranian militias in Syria.

So far, militias controlled by Iran have carried out at least two attacks on US bases in northeastern Syria, with two instances of US retaliation.

According to a report by the UK-based Syrian Observatory for Human Rights, the attacks left 19 dead, including three Syrian regime soldiers and 16 members of Iran-backed forces.

The Observatory said the attacks were carried out in the early hours of Friday local time by US fighter jets and drones, targeting positions of forces led by the Iranian Revolutionary Guards (IRGC) in Al-Bokamal desert, as well as other positions on the southern outskirts of Al-Mayadeen city and an ammunition warehouse opposite the “Officers Residences” in Harabesh neighborhood in Deir ez-Zur city.

The Pentagon said on Friday that the US military carried out the attack against militia groups who it blamed for a drone attack on Thursday that killed an American contractor, injured another, and wounded five US troops.

The US intelligence community assessed that the one-way attack drone was Iranian in origin, the military said, a conclusion that could further aggravate already strained tensions between Washington and Tehran.