Airstrike in Syria
Airstrike in SyriaiStock

A powerful Iraqi militia backed by Iran pledged on Thursday to get revenge for a deadly air raid on its fighters in Syria, blaming the United States or Israel for the attack.

Iraq's Hezbollah Brigades militia has said 22 of it fighters were killed in an air strike on Sunday on a military base in eastern Syria that reportedly killed more than 50 people.

Both Damascus and the Iraqi militia at first pointed the finger at the U.S.-led coalition fighting the Islamic State (ISIS) group in the area.

However, an unnamed U.S. official told CNN on Monday that the air strike was carried out by Israel and not by the U.S. or the international coalition fighting ISIS.

The IDF has not commented on the strike, as per its normal policy.

Hezbollah Brigades spokesman Jaafar al-Husseini said on Thursday it was still too early to say definitively whose forces carried out the strike, but insisted it "could only have been" the Americans or Israelis.

"When it becomes known who was responsible then there will be an appropriate response and the hand of the resistance will strike anywhere," he said during a memorial ceremony for the dead at a Baghdad mosque, according to AFP.

The Shiite Hezbollah Brigades are part of the Hashed al-Shaabi paramilitary units that battled ISIS in Iraq under the command of the country's prime minister.

The group has also been fighting for Assad across the border in Syria independent of the authorities in Baghdad.

Israel has in the past been accused of attacks in Syria. Last month, an air strike took place south of the capital, Damascus, and Syrian media said Israeli planes fired missiles at Iranian targets near Damascus.

In April, a military airbase belonging to the Assad regime near the Syrian city of Homs was hit with missiles. The Russian army, as well as Syrian media, claimed that two Israeli planes carried out the attack.

Prime Minister Binyamin Netanyahu has repeatedly warned about Iran’s presence in Syria. On Sunday, at the start of the weekly Cabinet meeting, he said, "We will take action - and are already taking action - against efforts to establish a militarily presence by Iran and its proxies in Syria both close to the border and deep inside Syria. We will act against these efforts anywhere in Syria.”

Iraq declared victory over ISIS late last year but the jihadists still control pockets of territory in Syria, where they are facing both U.S.-supported forces and pro-regime troops.

Sunday's strike hit a site that sits on a key route linking the Syrian-Iraqi border, and Iran beyond that, all the way west to the frontier with Lebanon.