Here's How the UK Inadvertently Armed Islamic State

WATCH: Inside the Islamic State

"The UK have ended up inadvertently arming IS," according to a new report released by Amnesty International.

The report claims that "irresponsible arms transfers to Iraq" and "multiple failures … to put in place oversight mechanisms during the US-led occupation after 2003" have led to the Islamic State building a sizable arsenal out of arms designed and supplied by a number of countries including the UK, US, and France, which the militant Islamist group have looted from Iraqi military stocks.

Oliver Sprague, Amnesty UK's Arms Programme Director, said: "The fact that countries including the UK have ended up inadvertently arming IS should give us pause over current weapons deals."

The report says the arms and ammunition used by IS come from 25 different countries, with a large proportion coming from the USA, Russia, and former Soviet Bloc states. Some of these arms were funded by oil barter arrangements, Pentagon contracts, and NATO donations. Their oldest piece of weaponry is thought to be a British 1914 Enfield Pattern bolt-action rifle.

Patrick Wilcken, Amnesty International's Arms Control researcher, said the fact that some of the weapons were so old highlighted "the dangers of weapons accumulation and proliferation that have resulted in mass atrocities across the region committed by Islamic State and other armed groups."

After Iraq's invasion of Kuwait in 1990 a UN arms embargo meant that imports decreased, but the US-led invasion in 2003 resulted in weapons flooding in again.

Amnesty today called for "all states to adopt a complete embargo on Syrian government forces."