Ahmad al-Hamidawi, the secretary-general of the armed faction, mourned in a statement the loss of a "great commander", Ali Hussein al-Freiji, who had joined the group more than two decades ago.

Two sources from the faction told AFP on Wednesday that a strike hit a vehicle near the group's main base in southern Iraq, killing two fighters.

The toll then rose to three, including the commander.

One source described the attack as a "Zionist-US strike".

The group's Jurf al-Nasr base was the first Iraqi target of strikes blamed on Israel and the US, which later expanded to other areas.

Since the start of the war, the strikes have killed 15 fighters, mostly from Kataeb Hezbollah.

Iraq, which has recently regained a sense of stability but has long been a proxy battleground between the US and Iran, had said it did not want to be dragged into the war. But it has not been spared.

Several Iran-backed armed groups -- known as the Islamic Resistance in Iraq, to which Kataeb Hezbollah also belongs -- claim daily drone attacks on US bases.

The Islamic Resistance in Iraq on Thursday warned European countries not to join the war, threatening their "forces and bases in Iraq and the region."

Earlier on Thursday, the Iraqi News Agency (INA) reported that security forces seized two rockets and a launchpad in the southern Basra province, that were set up to target a neighbouring country.