Wars launched by the US since the 11 September 2001 attacks have been estimated to have cost up to $4.4tn, according to a new study published by Brown University.

The study focused on the US-led wars in Iraq, Afghanistan and counterterrorism campaigns in Pakistan and Yemen.

The estimated financial cost of the wars stood at a minimum of $3.7tn and up to $4.4tn, which represents about a quarter of US current debt.

“Our estimate is larger because we include more than the direct Pentagon appropriation for the wars in Afghanistan and Iraq, and the larger global war on terror,” the study added.

Agence France Presse also quoted the study report as saying: “Wars always cost more than what the Pentagon spends for the duration of the combat operation.”

The US Government, however, had earlier cited the price tag for the wars at about $1tn.