THE United States has spent nearly $6 trillion (£4.6trn) on deadly wars in which at least half a million people have been killed since the September 11 attacks, according to a new report.

The Cost of Wars, published by Brown University’s Watson institute for international and public affairs on Wednesday, showed the scale of US military spending since it launched the so-called war on terror 17 years ago.

It found that the US has spent “an estimated $5.9trn (in current dollars) on the war on terror through fiscal year 2019, including direct war and war-related spending and obligations for future spending on post-9/11 war veterans.”

The report called for greater transparency and a comprehensive strategy to bring an end to wars, warning that high-level war-related spending was a national security risk as it was unsustainable.

The “war on terror” was badged as a response to the September 11 attacks, in which nearly 3,000 people died when mainly Saudi Arabian hijackers crashed planes into the World Trade Centre. It led to the US invasions and occupations of Iraq and Afghanistan and increased US military interventions elsewhere, including drone attacks in Pakistan.

The researchers said “between 480,000 and 507,000 people have been killed in the United States’ post-9/11 wars in Iraq, Afghanistan, and Pakistan.”

The study found that the “US military is conducting counterterror activities in 76 countries, or about 39 per cent of the world's nations, vastly expanding [its mission] across the globe,” adding that these operations "have been accompanied by violations of human rights and civil liberties, in the US and abroad.”

The death toll does not include those killed in Syria or other US-backed interventions, so the study acknowledges that the true figure is likely to be higher.