LONDON  - Islamic State (IS) militants 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 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 militants 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 militants 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.

Meanwhile, Syrian government warplanes killed at least 60 civilians including a dozen children in two days of air strikes on Islamic State-held territory at the weekend, activists said on Monday.

President Bashar al-Assad’s military has stepped up an aerial campaign over the last three months against Islamic State, an al Qaeda offshoot that controls about a third of Syria’s territory, much of it desert in the north and east. The air strikes have hit a number of Islamic State targets but have also killed many civilians in territory under the group’s control.

In Iraq, Parliament was to meet Monday under pressure to approve an inclusive government to win broad support against militants, as President Barack Obama prepares to unveil a strategy to defeat them. The outgoing government has faced criticism that by alienating the Arab minority, it helped create conditions that revitalised militants including the Islamic State (IS) militant group, which led an offensive that seized much of the heartland in June.

Meanwhile, the head of Egypt’s Al-Azhar said Monday that militants of the Islamic State were “criminals” serving a “Zionist” plot to “destroy the Arab world.” “These criminals have been able to transmit to the world a tarnished and alarming image of Muslims,” Sheikh Ahmed al-Tayyeb said.

“These fundamentalist terrorist groups, whatever their names, and their backers are colonial creations that serve Zionism in its plot to destroy the Arab world.”