London: Islamic State (IS) jihadists appear to be using captured US military issue arms and weapons supplied to moderate rebels in Syria by Saudi Arabia, according to a report published on Monday.
The study by the London-based small-arms research organisation Conflict Armament Research documented weapons seized by Kurdish forces from militants in Iraq and Syria over a 10-day period in July.
The report said the jihadists disposed of "significant quantities" of US-made small arms including M-16 assault rifles and included photos showing the markings "Property of US Govt".
It also found that anti-tank rockets used by IS in Syria were "identical to M79 rockets transferred by Saudi Arabia to forces operating under the (rebel) Free Syrian Army umbrella in 2013".
The rockets were made in the then Yugoslavia in the 1980s.
In neighbouring Iraq, IS jihadists seized significant quantities of US equipment from the Iraqi army when soldiers abandoned positions in northern areas when faced with a militant offensive in June.
The group captured a number of American-made Humvee armoured vehicles, which are now being targeted in US air strikes, and has reportedly used them in suicide bombings against Iraqi forces on at least two occasions.
The United States spent billions of dollars training and arming the security forces over a period of years, and both American and Iraqi officials repeatedly said they were ready to maintain internal security after US troops departed at the end of 2011.
Islamic State is also believed to have seized large quantities of weapons from Syrian military installations it has captured, including warplanes.