Unknown aircraft attacked a weapons depot belonging to Iranian-backed paramilitary forces in an eastern town near the Iraqi border early Tuesday, killing at least 10, a Syria war monitor and an Iraqi security official said.

The airstrikes took place in Boukamal, in the eastern province of Deir el-Zour. An Iraqi security official said the strike hit weapons depots belonging to Iraqi factions operating under the banner of the Popular Mobilization Forces, the name given for the mainly Shiite militias in Iraq that Iran supports.

The strikes are the latest in a series of unclaimed attacks both inside Iraq and along the border with Syria targeting Iran-backed militias. Last week in Syria, unknown warplanes targeted an arms depot and posts of Iranian-backed militias in Boukamal, killing at least 18 fighters. A Syrian security official said Israeli jets were behind the attack but denied there were casualties.

U.S. officials have confirmed Israel to be behind at least one of the attacks inside Iraq. Israel frequently strikes Iranian targets in war-ravaged Syria and appears to have recently expanded its campaign against Iran's spreading influence in the region.

The Britain-based Syrian Observatory for Human Rights and Deir Ezzor 24, an activist collective, said Tuesday's strikes occurred near Syria's border crossing with Iraq. The opening of the crossing, planned by Iraq and Syria, had been postponed several times in recent weeks.

Two Iraqi security officials confirmed the strikes, and one of them said initial reports suggested around 10 fighters may have been killed.

The Observatory, which monitors the conflict in Syria through a network of activists on the ground, said the strikes caused significant human and material damage. It said at least 10 Iraqi nationals from militias loyal to Iran were killed. It added that the strikes targeted a missiles and ammunition depot in and two other locations in the area.

It said the number of killed is likely to rise due to the serious nature of the injuries.