DAMASCUS, March 5 (Xinhua) -- The U.S. forces started to deploy new defense systems in its bases in northern and eastern Syria to protect against any possible attack by Iran-backed militias, a war monitor reported Friday.

Anti-drone air defense systems and surface-to-surface missiles are being deployed in the al-Omar oil field located in the countryside of Deir al-Zour Province in eastern Syria, said the Syrian Observatory for Human Rights.

The U.S. forces are bringing the new equipment from its bases in Kurdish areas in Iraq, the Britain-based watchdog added.

More defense systems will be deployed in the coming days in all U.S. bases in northern and eastern Syria, noted the Observatory.

This comes days after a U.S. air strike on positions of Iran-backed militias in eastern Syria that killed more than 20 fighters, which was launched as part of the retaliation for the attacks allegedly carried out by Iran-backed fighters against U.S. positions in Iraq's Erbil.

The Syrian government has repeatedly urged the UN Security Council to push the U.S. forces out of Syria, saying their presence is illegal.