Shiite fighters take part in an intensive security deployment against Islamic State militants in Balad, north of Baghdad.

Islamist militants have brought dozens of fighters from the eastern Syrian city of Deir al-Zour to Iraq to join them in their fight against security forces, Al Sumaria News reported activists as saying on Saturday.

Without specifying an exact figure, the Syrian activists said that the Islamic State of Iraq and Syria (ISIS) group brought dozens of Deir al-Zour residents “to participate in battles on different fronts including the Iraqi forces and the [Kurdish] Peshmerga.”

The news come after the Pentagon said on Friday that ISIS militants are having to spend more effort defending key supply lines in Iraq due to U.S.-led air strikes and pressure from local forces.

ISIS’ supply routes into Iraq from neighboring Syria have become a central focus of combat, with Iraqi government and Kurdish forces — along with coalition warplanes — seeking to disrupt and cut off the militants’ access to weapons and equipment, spokesman Rear Admiral John Kirby told reporters.

“They’re trying to protect what they can hold onto now, and… also we’re seeing them put a lot more emphasis on protecting their lines of communications,” Kirby said. “That’s where they’re putting their energy.”

U.S. officials say the Iraqi government army is being trained and armed to stage a major counter-offensive later in 2015, but in the meantime, the international coalition is seeking to pile pressure on ISIS supply lines.

“If you look at the air strikes we’re conducting, and you look at some of the operations that are being done by Iraqi and Kurdish forces, you can see that we’re trying to disrupt their ability to do that, to preserve those lines of communication,” he said.

“One of the keys for them to maintain the control they have is to be able to sustain themselves, and we’re trying to make that as difficult as we can for them.”

However, it was unclear if the ISIS group had faced serious difficulty resupplying its fighters as a result.

U.S. reports 11 anti-ISIS air strikes

Meanwhile, the U.S.-led forces launched five air strikes near Kobani, Syria, and six in Iraq since Thursday in their battle against ISIS, the American military said.

The strikes in Syria hit several ISIS fighting positions, two tactical units and destroyed a building, according to a statement from the Combined Joint Task Force. The strikes in Iraq hit near al-Qaim, al-Asad, Sinjar and Mosul.

After nearly 1,700 air raids by U.S.-led forces since Aug. 8, ISIS’ advance has been halted for the most part but the jihadists have held on to much of the territory they seized in Syria and Iraq last year.

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