ISIL, a splinter group of Al-Qaeda which wants to set up a so-called Islamic caliphate encompassing both Iraq and Syria, triggered insurgency in Iraq in the past two weeks, taking control of the northern city of Mosul and some border crossings with Syria.
Its advances in Iraq appear to have spurred on the Syrian branch, which is fighting both the Syrian army and also rival insurgents such as the Western-backed Free Syrian Army (FSA).
ISIL terrorists seized Syrian towns near the Iraqi border from rival militants last week.
For the first time, ISIL terror elements have been using US-made Humvees - four-wheel drive military vehicles - in fighting in northern areas of Syria's Aleppo province, the British-based Syrian Observatory for Human Rights said on Sunday.
The vehicles, which appear to have been seized during ISIL's recent Iraqi offensive, were used to gain control of villages outside the town of Azaz, close to the Turkish border, it said.
The Observatory said ISIL in Syria had been supplied with dozens of the vehicles from Iraq.
The United States has long supplied Humvees to the Iraqi army, which has been fighting an increasing violent insurgency since US forces withdrew at the end of 2011.
ISIL terrorists in Iraq have often seized abandoned military equipment from Iraqi forces, including armored vehicles.
Syria has been gripped by deadly violence since March 2011. According to reports, Western powers and their regional allies - especially Qatar, Saudi Arabia, and Turkey - are supporting the militants operating inside the country.
NTJ/MB